Water-cooling vs block of aluminum
Just doing a deeper test with measured comparison between a cheap water-cooling setup and a block of aluminum. Using a Pixel 4a and a free Android app called "Burnout Benchmark".
Results indicate the water-cooling works slightly better than a block of aluminum, although the phone does still throttle under constant heavy load regardless. Both options work much better than doing nothing.
Conclusion? If you're publishing HD video or playing games using your phone for a lengthy period of time, something like a phone case with a built-in heatsink might be a helpful way to erk out a few extra frames-per-second.
Water-cooling is fun and all, but the benefits of it vs the practically of other solutions is debatable.