When Future Trunks first arrived on the scene, fans were left speechless when they saw the young Saiyan from the future take down Frieza without even breaking a sweat. While he meant well, traveling to the past to warn Goku and the others about the Androids led to the creation of two very different Dragon Ball timelines: one in which Androids 17 and 18 ravaged the Earth (Future Trunks' timeline), and another where they became productive members of society (the main timeline).
There are many other differences between these timelines, with one of the biggest being that certain characters are much stronger in one timeline than they are in the other.
10 Weaker: Android 18
Though she's not as strong as Android 17 in the main timeline, training with Krillin has enabled Android 18 to further refine her own techniques, as well as steal some from her husband's arsenal, like his Destructo Disc. The Android 18 of Future Trunks' timeline couldn't lay a hand on Future Trunks after he returned from the past. At that point, Future Trunks was no stronger than a Super Saiyan 2 but was a lot stronger than a fresh Super Saiyan.
While Android 18 currently isn't as strong as a Super Saiyan 2 herself, she's definitely a lot stronger than she was during her debut in Dragon Ball Z. During the Tournament of Power, she managed to defeat Ribrianne, who could trade blows with Super Saiyan Vegeta, and before that, she held her own against Super Saiyan Goten and Trunks during the 25th World Martial Arts Tournament. We doubt Future Android 18 could accomplish either of those feats.
9 Stronger: Yajirobe
In the TV special The History of Trunks, fans were led to believe that Yajirobe had been killed by Androids 17 and 18 in Future Trunks' timeline, but in Dragon Ball Super, it was revealed that he actually survived after Korin gave him his last Senzu Bean.
While Future Yajirobe is still a coward who shies away from a fight, living in a war-torn world has definitely done him a favor. He might not be on the frontlines as much as he should be, but he made himself useful for once after saving Goku and Future Trunks, retrieving them from right under Goku Black and Zamasu. Even if he's just a tiny bit braver, stronger (his arms are more muscular in the future), or faster, it's clear that this alternate timeline has given him a greater sense of agency that the main timeline's Yajirobe will never develop so long as there are other Z-Fighters to do the dirty work for him.
8 Weaker: Cell
After absorbing Androids 17 and 18, Cell became so powerful that it took an entirely new form of Super Saiyan to take him down.
After Future Trunks destroyed the Androids in his own timeline, Future Cell was stuck in his Imperfect Form, which was so weak in comparison to his Perfect Form that Future Trunks was able to take him out without even transforming into a Third Grade Super Saiyan.
7 Stronger: Trunks
Future Trunks and the young prepubescent Trunks of the main timeline may be different characters, but they're the same exact person, despite some major personality differences. Still, there's no denying that Future Trunks is definitely stronger than his counterpart in the past.
While Future Trunks grew up in a world constantly ravaged by powerful threats that forced him to reach new levels of power just to survive, Trunks grew up in peaceful times. Even when powerful foes like Buu and Beerus threatened to destroy the planet, he could always count on Goku or Vegeta to save the day. Future Trunks not only discovered how to tap into the powers of Super Saiyan 2 all on his own, but he also mastered a Super Saiyan Rage transformation that enables him to compete with someone as strong as Super Saiyan Rosé Goku Black.
Trunks, on the other hand, can't go beyond Super Saiyan unless he's fused with Goten.
6 Weaker: Android 17
Just like Future Android 18, Future Android 17 was killed by Future Trunks after he returned from the past. Android 17 is far weaker in Future Trunks' timeline because he never got the chance to grow into the powerhouse that he is in the main timeline.
Android 17 has become one of the strongest Z-Fighters to date, able to fight alongside Super Saiyan Blue Goku and Vegeta without getting in the way. He not only won the Tournament of Power, but he played a pivotal role in Jiren's defeat.
5 Stronger: Zamasu
The main timeline's Zamasu could barely hold his own against Super Saiyan 2 Goku. Fortunately, he was destroyed by Beerus before he had a chance to enact his sinister plan to kill all mortals in the multiverse. The Zamasu of Future Trunks' timeline, however, was able to provide a significant challenge to even a Super Saiyan Blue.
While this can definitely be attributed to his immortality, the fact still remains that it took more firepower to deal with Future Zamasu than it did his weaker counterpart in the present.
4 Weaker: Goku
After witnessing Goku continually shatter his own limits throughout the series, it was almost ironic to see him fall victim to a measly heart virus in Future Trunks' timeline.
The Buu Saga showed that Goku could still train and grow stronger in Other World, so even in Future Trunks' timeline, it's possible that he could've reached Super Saiyan 2 and 3 on his own, but without his encounter with Beerus and Whis, he would never learn to tap into his dormant Super Saiyan God powers.
3 Stronger: Bulma
While Bulma isn't a fighter, it's clear that her future counterpart is just a bit more technologically adept. Future Bulma designed the Time Machine that Future Trunks used to travel back to the past. After it was destroyed by Goku Black in Dragon Ball Super, present-day Bulma was left to repair the moss-covered Time Machine that Cell left behind all those years ago.
This wasn't an easy task, and Bulma even gave her future counterpart some credit for designing such a complicated machine. It's clear that the pressure Future Bulma was always under forced her to tap into unknown reservoirs of knowledge that the Bulma of the main timeline used to plan parties instead.
2 Weaker: Gohan
After the death of the other Z-Fighters in Future Trunks' timeline, Gohan was left as Earth's sole defender against Androids 17 and 18. Although he'd mastered Super Saiyan without the aid of his father, his power wasn't enough, and after a hard-fought battle, Androids 17 and 18 finished him off.
Future Gohan is most likely training in Other World with Future Goku, but since he never crossed paths with Old Kai, his latent power would've never been brought to the surface. Gohan's power may have taken a sharp decline throughout Dragon Ball Super, but after reawakening his full potential for the Tournament of Power, he's just as strong as he was during his fight against Super Buu, placing him leagues above Future Gohan.
1 Stronger: Mai
Out of all the plot twists that Dragon Ball Super brought, one of the biggest might be the inclusion of Future Mai as a valuable ally, and romance, for Future Trunks. When she was working alongside Pilaf and Shu, Mai couldn't take down Goku when he was still a child back in Dragon Ball.
Fast-forward several years later in Future Trunks' timeline, and she's at the head of humanity's armed resistance against Goku Black. Despite lacking the ability to fly and fight with ki blasts like Future Trunks, she's been able to hinder Goku Black and Zamasu with smoke bombs and pinpoint rifle shots. Without her leadership, we can't imagine the people of Future Trunks' timeline would have the heart to keep fighting.
The Mai of the main timeline is nowhere close to her future counterpart's level. She's still following Emperor Pilaf! As long as she remains under his command, she will never grow into the leader that we never expected her to be.