All true, however, (splitting hairs, yes), the reason FH9 can best the shuttle boosters is because they had to carry the shuttle itself, which was around 50 tons.
The only non-reusable part was the external fuel tank.
But yeah, sending something as big as a bus up and down was probably the bane of it.
But to use them again a lot of efforts had to be spent, comparing to what's possible with first stages of F9. That's why Shuttle boosters are called refurbishable.
It turns out not having to "shuttle" half a dozen humans up to orbit every time you want to get something up there is a good idea.
At minimum, each mission had a commander and pilot. Then there were missions specialists and payload specialists, which depended on the specific mission the shuttle was carrying out.
There's always a lot of work to do, so it makes sense that they'd maximize for productivity.
Remember the shuttle "had to" be all things to all people, and the military demands ended up being VERY heavy and expensive.
At this time AFAIK nobody has the technical ability to snatch a Soviet spy sat and take it home, or haul strange and heavy (many ton) electronic warfare payloads over a target and land next orbit on NATO turf. Now, WHY you'd want to, or SHOULD you want to, are outside the bounds of this discussion, but the shuttle certainly had that kind of military stuff as a very expensive and very heavy design req.