Skills don't make any difference above having markdown files to point an agent to with instructions as needed. Context7 isn't any better than telling your agent to use trafilatura to scrape web docs for your libs, and having a linting/static analysis suite isn't a harness thing.

3.7 was kinda dumb, it was good at vibe UIs but really bad at a lot of things and it would lie and hack rewards a LOT. The difference with Opus 4.5 is that when you go off the Claude happy path, it holds together pretty well. With Sonnet (particularly <=4) if you went off the happy path things got bad in a hurry.

Yeah. 3.7 was pretty bad. I remember its warts vividly. It wanted to refactor everything. Not a great model on which to hinge this provocation.

But skills do improve model performance, OpenAI posted some examples of how it massively juiced up their results on some benchmarks.