Thank you so much for sharing your experience! I just received the 13” warranty replacement (after 2 weeks waiting) and, although it throttled less, I was still dissatisfied. So it does appear that there is some thermal vatiability between the 2 units I have.
Microsoft had been giving me conflicting information on if the 15” had a fan—thanks for confirming it did.
I just requested a refund successfully and ordered a 15”. As a note, the return window is now 60 days. Here’s hoping I can stay with a surface! I will post back next week with my experience.