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.