What do you even mean as serious contender? I’ve been using Linux for almost 15 years without an issue on CPU, and I’ve used it almost only on very modest machines. I feel we’re not getting your whole story here.
On the other hand whenever I had to do something IO intensive on windows it would always crawl in these machines
What are you on about? Yes they made sure their gadgets were easy to use, but Apple and Jobs were the pinnacle of “locking you in” on their ecosystem for the profit of it. Sure they weren’t as careless about users when compared to Microsoft but they weren’t too favourable of you using anything else. They invented this stuff.