I had a similar experience with a Dell Latitude 7280 (i5 7300U, Intel 620 graphics, 8gb RAM, UEFI boot) a few months ago. Like you, I don't do anything too taxing on the computer (Firefox browsing with 3-4 tabs open at a time, short (4-8 minutes) YouTube videos, word processing and spreadsheet work, and some network maintenance).
The laptop ran smoking hot running Solus. I was unable to identify the issue, having checked processes and performance with System Monitor, checked out the battery (excellent condition, no issues) and followed up tips and suggestions from Linux forums. Nothing worked. I eventually removed Solus and used the computer for other purposes after a clean install of Windows.
Last week, because I needed Linux functionality on a laptop to do some network maintenance for a small railroad museum where I volunteer, I did a clean install of Solus on the same Latitude 7280, then installed all current updates. During the update processes, the computer ran warm, as expected, but not hot. I've been using the laptop steadily for 5-6 days now, and it is running cool, a bit warmer than it ran using Windows, but not significantly warmer.
I have no explanation at all about why the laptop used to run smoking hot and now runs cool. The Solus setup is identical (stock Solus 4.1 Budgie, remove Thunderbird, add tlc, gufw and a few network maintenance tools, no third party drivers). The only variables seem to be (1) Dell updated the laptop's BIOS/firmware about a month ago, (2) the Solus build (with all current updates) is newer now than the Solus build I used last summer, and (3) the Linux kernel (I believe) is newer.
As a point of reference, I've experienced no heat issues on my desktop (Dell Optiplex Micro 5070, i5 6600T, Intel 530, 8gb RAM, UEFI boot) or a Dell Inspiron 11-3180 laptop (AMD A9, onboard graphics, 8gb RAM, UEFI boot).
I'm thinking (without any hard evidence to point to) that it is possible that something in the earlier Solus build wasn't interacting properly with the laptop's hardware, and now, for whatever reason, the newer Solus build is interacting properly. I wish I had something more concrete to offer.