But such a transaction makes it completely obvious that is what the miner intended to do, whereas one which sends a small amount to another address and a huge amount in fees can be plausibly denied as "I fat fingered the fee" or "I was trying to code a transaction manually and forgot to specify a change address, and so everything was taken as a fee".
True. Dumb subjection requires dumb solutions. So, better just avoid the merchants all together, whenever that's possible. I haven't once been told to have tainted coins, even though I mix regularly.
Also, one more reason they don't taint block rewards is because every bitcoin user is part of it, and as you said they associate every input with every output, hereby if one user is a suspect, every bitcoin user from that block becomes also a suspect, same as with mixing. And since everyone can't own tainted coins (although with AML they are all tainted until proven clean) as this would make tainting further pointless (because if all are tainted there's no taint), their analysis begins from the moment these brand new outputs are spent.
The funny part is they don't care (or care little) for blackmailing users with tainted coins. The real power comes from controlling bitcoin users who just want to complete verification, and who suddenly feel responsible for someone else's actions (if they take the time to read what's a tainted bitcoin).