If you encrypt at a block level then the pre-authentication parsing code is relatively simple. If you encrypt on top of a filesystem, it's more complicated and relatively likely to have vulnerabilities (seen in practice in iOS at least). It may not be that important, but it's a factor.
Sure, but it's also the case that encrypting at the block level means that upper-layer filesystem code needs to be prepared to deal with corrupted metadata, which is stored in encrypted sectors that attackers can randomize.
The LRW paper has some starting points for tweakable ciphers with random access properties. Note that if you're doing filesystem encryption, you have a place you can put a nonce to do randomization. For that matter, you could divide files up into 4k pages and use OCB for the pages.
I don't think I understand your point about handing filesystem drivers untrusted data.