in order of those above
1. obvious fact
2. is heat really so much of a problem that we need to overthink it (i.e controlling it via dimming?)
3. when i say switch off 1/N of the cobs, probably 1/N of the drivers would be more appropriate (well easier, at least)
lets say you have a space of 8 bars with 6 cobs each, each bar on its own 200W driver. at appropriate distance to canopy so that light is relatively uniform (no lenses)
at 85 degrees one of the drivers kicks off with a simple thermostatic switch, and you 'dimmed' from 1600W to 1400W
at 87 degrees you drop another driver and youre at 1200W, etc
as an extension of this build a simple circuit on a B version of the meanwell that uses a few fixed resistors in parallel, some of the relays are triggered by relays to change from 100% to 70% current.
the 'logic' in this case could be as simple as a cheap bimetal wall thermostat