Thank you for the question. It helps me to understand the potential issue. Let's start at a $100 fee level. Say bitcoin gets to $100,000. Moving 0.2 bitcoin would incur a 0.5% fee. What do you think of these numbers? I am okay with federated solutions for smaller amounts.
Discussion
The problem is that if bitcoin keeps getting a lot more adoption, everyone will get priced out, specially ppl in the third world, even L2 like LN or Liquid will take a hit if base chain fees are too high. Don't forget we already had a "block increase" with segwit otherwise fees now would be a lot worse. Custodial solutions and many L2s will always play a part but sooner or later base layer will need to increase so that L2s can also be smoother. I think the only question is how is the block size increase done.