Trafalgar Law is certainly a powerful pirate in the One Piece world. His physical strength, proficiency in Haki, and awakened Op-Op Fruit put him on par with the likes of Eustass Kid and Monkey D Luffy. He's more than qualified to make a name for himself in the New World and is even a candidate for finding Gol D Roger's legendary treasure.
Unfortunately, Law's capabilities are not a reflection of the capabilities of his crew. The Heart Pirates as a whole don't come off as all that strong. If Law is in a one-on-one match, then it's a safe bet he'll do well. However, if the Heart Pirates ever had a crew vs crew match like the Straw Hat Pirates tend to have, it would be difficult to say that they'd all come out on top.
Can Law Count On His Crew?
This exact crisis has made itself apparent in Chapter 1063, "My Only Family." As of this chapter, the Heart Pirates have been forced into a confrontation with the Blackbeard Pirates. This will be Law's first time going up against an Emperor without the backing of an alliance.
Many fans are expecting Law to lose this encounter. Even the ones who believe Law can hold his own against Blackbeard are expecting the rest of the Emperor's crew to gang up on him; it would effectively be a repeat of what happened when Whitebeard tried to attack him. As for the rest of the Heart Pirates, they're all expected to lose outright to Blackbeard's men, so they won't be able to defend Law.
Part of the problem with facing the Blackbeard Pirates is that the crew is too strong. Each of Blackbeard's most trusted subordinates is powerful enough to be the captain of their own crew. Anyone hoping to win against this Emperor-level crew will need a similarly powerful crew.
Unfortunately, it's a mystery how Law's crew would hold their own against any pirates, let alone Blackbeard's. Of the Heart Pirates' 21 crew members including Law, only eight of them even have names; the rest of the crew is so faceless that Pandaman was able to sneak into a group shot. Of the eight named Heart Pirates, only Law, Bepo, and Jean Bart have proven themselves to be exceptional fighters. If there's something Shachi or Penguin can do to beat back the likes of Van Augur or Doc Q, it hasn't been revealed yet.
For all anyone knows, Law has been carrying his crew all the way through the Grand Line. It would be like an RPG playthrough where only one character receives all of the level-ups and power-ups. Similarly, Law may be dealing with most of the Heart Pirates' opponents so that the rest of his crew doesn't have to. However, unless Law far surpasses everyone on the enemy side, he's in for the fight of his life.
What Does A Strong Crew Look Like?
It would be more ideal to have a well-rounded crew like the Straw Hat Pirates. They might not all be on the same level as their captain, but they're all definitely strong enough to hold their own in a tough battle. They can even be trusted to beat the enemy's commanding officers so that Luffy doesn't have to worry about getting attacked by them while going after their leader. This is why when the Straw Hats presumably go up against the Blackbeard Pirates, everyone will be trusted by the audience to fight and win in one-on-one battles.
As for Law, the expectations for his odds against Blackbeard are optimistic at best. Even if the Surgeon of Death can somehow win, the Emperor's men will likely gang up on him after dealing with the rest of his own men. If Law had a stronger crew, his odds might seem more favorable. As things stand, however, he should probably escape as soon as he can.