I don't expect emails to get through to busy CEOs of huge companies like Apple unless you're really lucky and they make it through some automation, but I have dropped him an email just in case. I guess you never know.

He has an army of people that would read his emails. A truly important one should get read.

You could always try calling, too! I cold called Marc Benioff at Salesforce and he actually picked up the phone.

I did it once, I'm pretty much sure Tim did not read the email, why would he, someone in his team did. I had an awful experience with AASP, no computer, no fix, no timelines (and money was tight), tried to escalate as much as I could and failed. Wrote to Tim Cook, explaining my situation and attaching all references... Got a call from Apple within like 2h, got a brand new Mac in a day. Those emails do work.

Has anyone tried sending an email to Nadella telling him that Windows is terrible now?

What if that was all it took.

I once had a terrible experience dealing with my local Apple Store and then a hostile call with an Apple Retail manager after I left critical feedback.

I emailed Cook, mostly just to shout into the void. Within a week I got a call from Apple Corporate, they gave me an appointment the next day and my hardware issue was suddenly solved over-night.

Helps if there are support case numbers with attempted diags, maybe.