What are you doing to get your 16 Pro to heat up “pretty frequently”, out of interest?
With my 15 Pro and current 16 Pro Max I have recorded hours of ProRes Apple Log video, even filmed 4K 120fps video using an external drive attached and honestly can’t think of a single time it’s got hot or lagged.
The only time it’s got very hot was during the summer heat when outside and my phone on the table/grass in sunlight. But that’s just me.
As a side note, I believe the Air’s frame acts as a heat sink, channelling warmth away from the densely packed plateau - this is enhanced on the Air by the Copper Post dissipation system, by spreading the heat across the chassis unlike the 15/16 Pro set up which is less efficient.
Your fears are reasonable, especially before we’ve seen reviews, but EU data and early hands on impressions do suggest otherwise. There were no heat-related penalties in the EPREL results and it has Class A for mixed-use endurance.
It may throttle sooner than the 17 Pro/Max for intensive gaming or maybe like I dunno, serious video editing? But it’s still looking like it’ll sustain performance longer than the 16 Pro under similar loads. I reckon most users won’t push these limits regularly (80%). Of course, you are quite probably in the 20% that might and that’s why you need a Pro model.
Nothing further to add on the speakers - if you watch video/listen to music all the time on your iPhone and use the on board speakers, then yeah, it’s not the phone for you.