When it comes to measuring how much heat is happening to the clear unobstructed glass in a refractor, sure, the transmission is very high so that energy isn't going into the glass and it's fine. But, what it hits at the end of that refractor is not fine. This is where lots of us have broken things. Also, little apertures don't produce the same load that a large aperture does. There's a big difference between a 60mm, 80mm, 150mm, 200mm, 280mm, etc when it comes to that. A lot of the information is largely based on refractors where you're just passing light through glass that has incredibly high transmission so that glass isn't absorbing that energy, just passing it on.
This doesn't work when you apply it to the SCT or reflector design. Point that at the sun, big aperture, without anything other than a little UV/IR cut filter and something is going to get damaged. If nothing else, you can melt whatever is at the end of your imaging train real quick.
I've cracked KG3 filters with 150mm aperture, filters made to absorb IR energy. And my eltaon(s) & cameras without a front mounted ERF at 150mm overheat (goes offband). And again, tube seeing is a real thing (same reason planetary imagers don't want tube currents). Having a bunch of heat transferring around in there is bad for seeing. I've experienced that at 150mm with only a UV/IR block filter and the seeing limitations were very apparent (and solved immediately with a front mounted ERF to keep most of it out to begin with).
And like your example, pointing a big aperture oil spaced triplet at the sun for a while will not go well likely for a long time.
Monday, I will have my filter-cell in hand to setup a SCT with a tri-band 214mm narrowband dielectric filter (serving as a full aperture ERF). I'll do some measurements and compare to my 150mm with it's ERF setup. Currently, my 150mm refractor setup puts a 120F beam (unfocused) onto some paper when I measured it last (not enough to start combustion). And that's what I image with.