Bartolomeos devil Fruit is by far the most overpowered in the series. And the only reason why he made it to the new world.

Hard to know if that's the case, it certainly helps him significantly. It shapes his character and actions. It might be if he had no Devilfruit he would simply fight differently, most fruit users would.

He can block all possible attacks coming straight to him and his allies by just crossing his fingers and creating a barrier, no matter how strong that attack may be the barrier never breaks.

This one, I doubt. For several reasons, some which can be seen in the story and others which can be inferred.

For starters he couldn't stop Doflamingo's Plot-cage.. ahem, I mean bird-cage. It continued to move despite the barrier however people pushing his barrier into it seemingly slowed the progress of the cage. This means that with enough force the barrier will move, so it's very unlikely it can simply block all possible attacks, if struck hard enough the barrier might simply be smashed right back towards him.

We know for a fact the Barriers don't stop sound waves. He's been enclosed by them and had conversations with others back/forth. This means there are attacks which can pass right through his barriers, Apoo being a big example or anyone with meaningful sound based attacks. Light attacks can work in the same way. Unsure if Kizaru could outright ignore his barrier for example, but we know he can be blinded through it due to not blocking light.

Despite his barriers having limited surface area, his barriers are never paper-thin. Which if he was possible of doing would result in much bigger areas covered with the same amount of material. While not proven this suggests there's a reason for this, indicating thinner barriers would be less effective or there's a hard limit on how thin he can make them. We cannot tell for certain if it's artistic license or not but--- we can see his barriers are much thicker when he prevents major attacks than when he uses them as stairs for example. So this suggests at least another potential weakness.

Other than the 'sound' issue One Piece has a whole series of abilities that can target areas or entirely negate a barrier due to their large areas of effect, shockwaves or attacks which are less direct / more nebulous.

e.g. Fujitoras gravity would very likely pass through the barrier or ignore it entirely. Robin could strangle or hold him despite him being behind the barrier, including forcing him to un-cross his fingers canceling the barrier out. Caesar Clown could remove the air in and around the barrier.

There's also loads of unseen, untested stuff that would be really interesting to see with his barriers. For example: I'd love to know if Mr. Pink could swim through his barrier. Could Diamante make the barrier like cloth? Could Wapol eat it? Could big Mom steal lifeforce/soul through it? etc.

Bartolomeo can easily kill enemies by surrounding them by a barrier and slowly crushing them to their deaths.

True. However Doflamingo could clearly counter this and he's considered weak by Yonko standards. Law could shambles out.

While I think overall Bartolomeo has a very strong fruit, I put it more in categories with characters like Magellan or Law. Fruits that in theory could be pretty lethal to 99% of enemies and yet, don't appear to be used that way. Either due to limitations they have we don't know about, plot reasons or because after a certain point or due to a specific mechanic more powerful characters simply aren't impacted by it. e.g. Katakuri could see it coming and never get enclosed by a barrier or have his heart removed. Kaido might simply break a barrier or be too tough to have his heart removed or Haki that's too tough etc.

I mean both Magellan and Law have fruits that are essentially 1 hit kills in all but the most outlandish situations but I see Kaido, Shanks, Blackbeard etc all doing fine.