The thing that tickles me is that it has to slow down to reach terminal velocity rather than the normal way of thinking about objects speeding up to reach terminal velocity.

Wait a minute; we've been lied to!

I’m probably missing something important here, but isn’t this true of most things that de-orbit into an atmosphere?

Yes, but that's not the case for most objects you interact with in everyday life. All, most likely, unless you're in a particular job.

They're comparing to the average falling object not the average de-orbiting object.

not missing anything, but it's just one of those things about how fast orbital speeds are. yes, i know orbital speeds are around 17,000 mph. this is just another example of just how fast that is. a lot of people might be familiar with falling objects speeding up to get to terminal velocity which is kind of a speed limit for normal things. for de-orbiting spacecraft, this is just another milestone of slow speeds to achieve and not a limit of how fast it goes.

sometimes just looking at things from a different perspective makes me smile on the relative nature of "fast"

The boosters never achieve close to orbital velocity though, less than half if my memory is correct.

it's a good thing nobody was confused about the booster vs ship re-entering the atmosphere

I’m not a scientist, but is it not at terminal velocity for most of the way down by definition? So it’s not slowing down to reach terminal velocity, it’s just that the resistance becomes higher thus reducing terminal velocity?

Terminal velocity is the fastest speed it would accelerate to via the pull of gravity versus air resistance. In space, there is no air, hence no terminal velocity.

If the object is heating up due to air resistance (and compressed air), then it's moving far faster than terminal velocity. The heat is from the air getting compressed and slowing it down.