skills and agent.md are very portable though? I figure at most, as the models get better, the only maintenance you need to do is pare them down to remove unnecessary context.

I mean, I wouldn't know how portable they are between models because I don't use them. I don't use them because, well, I don't need them. I mainly use LLMs as a StackOverflow replacement via the Web chatbots.

I only use CC or Codex for a quick MVP once every few months or so.