Sure, but would the players notice that it is some special block that costs him performance? Without FPS display they might only notice this at the next horde night when suddenly FPS starts to drop to unplayable levels. And then making the connection to having placed a lot fo those blocks in the week before? We here might have a good chance making the connection since we have heard of high polygon blocks being a problem. The typical player has almost no chance.
Is there an automatic way to count block polygons? If not, they need to make a list of all say >1000 blocks with their polygon count. And a performant routine evaluating a chunk that needs to be called every time a block is placed. Just saying this isn't work done in a day. But sure, possible and a win for everyone.
With the barrels I could imagine it isn't for their poly count but for there effectiveness as bombs. Or just an oversight. But I don't think they are containers, at the moment you would not be able to store gas in them