Miners care about the whole block reward, not only transaction fees. A higher block rate means they can claim more of the subsidy, and possibly more fees. Note also i said it would bring (all others things equal) fee rates down, i did not say anything about total fee revenues.
I agree it would make it much less likely than with today’s incentives, but i wouldn’t be as confident as to rule it out entirely. Mining today is extremely concentrated, and the most part of miners’ revenues (block subsidy) is decreasing exponentially. Of course it would not be marketed as a 51% attack, how about a “miner activated fee rate easing” whereby miners get more revenues and users get lower fees? Note also it’s not strictly necessary to reorg out the blocks of honest miners to exploit this, especially with a large share of the network hashrate participating.