I'm not really going to get into whether people can select seats in advance for basic economy. But I will address the OP's question about whether travel cards are still worth it.

For me, yes. I got into this hobby back in early 2014 and have accumulated millions of miles from churning. I've been to 35+ countries in the last 4 years and that wouldn't have happened without all the miles I've racked up. Even now, almost 5 years after I got into the hobby, I still have a huge stash of points and miles that I can use.

I've slowed down a bit. Banks have gotten smarter about putting in rules to limit the amount of gaming the system that people can do. I still do it when able.

So for me, travel cards are still absolutely worth it. But I'm certainly not as crazed about it as I use to be.