Yes those other platform have it, as does Suf. All of them implement it in it’s basic unaltered form. Although, you mention Coggan but if you actually read his postings he doesn’t like the way it is blindly used due to the inherent flaws and he’s the co author of the original model. It’s basically one of those uncontrollable beasts now. All the experts and platforms know it’s flawed, but because so many people use it they basically have to add it.
Your example of using TSS to compare rides is actually it’s single biggest flaw as unless they are the same type of ride, comparing two 80 TSS rides for example can be very misleading. Time in zone and specific intervals is generally a much better way to compare rides and again, only if they are of the same type.
I think the issue boils down to the desire to boil what is actually a very complex system down to a simple number. Although in reality, the differences you get with TSS based on your own profile are unlikely to be hugely different unless you are significantly skewed left or right on the power scale. So spending a lot of time trying to manipulate/shoe horn two totally different models into one will likely still result in a set of numbers that have their own set of flaws.
One thing’s for sure though, 4DP will never be merged with TSS as the final number as TSS is trademarked by the PeaksWare group and 4DP wahoo/Sufferfest so it’d be a bit like Specialized suddenly selling bikes with Bontrager wheels
But these are just my ramblings so feel free to take them with a pinch of salt