I think there might be a few things to consider here:
1. Is it without any loss in productivity? Or are they so productive/skilled that they can still outpace most other devs even without the IDE's additional functionality?
2. Is there a loss in productivity, and they just don't realize it? Just because they can still do a good enough job without an IDE doesn't necessarily mean that they couldn't do a better job as experienced IDE users.
This is similar to the arguments people make against using Rust. "I can code C just fine and never have any issues, I don't need Rust"
It's also similar to this Copilot discussion. The people who say "I don't see any benefit from LLMs when coding", could it be that they just... don't have enough experience using LLMs? We've -just- had that come up in HN[0], where everybody in the comments was showing how they got the answer just fine out of their LLM of choice, while the OP was all about how AI couldn't possibly understand that bit of code.