Did you know that you can move things between drives? No one plays their entire Steam library at the same time, but I can store much of it ready to play on large-capacity HDDs, which are dirt-cheap. If I suddenly got back into Skyrim again, I'd spend a few minutes moving it to one of my SSDs.
I tend to agree for most things, but modern Blizzard titles are near unplayable without SSD because of they way that they load assets. You'd be technically in the game, but half of the models take 5 minutes to load in.
The are other games that load in things like this, but I can't think of them off the top of my head.
Honestly......spinning disks are good for anything. Yeah I don't have any in my gaming rig but my NAS is only spinners. Cheap and fast enough.
It all comes down to how much money you have. If you can only afford spinning disks, then get them - and enjoy your gaming. If you can afford faster drives then great, good for you!
I used to think this too until I got a proper NVME (instead of another SATA SSD). Once you get used to programs opening instantly—and no loading screens in games, ever—there's no going back to spinning disks. Waiting 10-20 seconds for a program to open on a HDD feels like an eternity now.
100 GBs is mid-tier modding nowadays. That's where you stop if you want Skyrim to still be Skyrim instead of a game made in the last 5 years that is actually good.
Spider-Man 2 got a PC version, but it was a completely different game from the more well-known console versions and wasn't nearly as good. A linear progression of levels instead of an open world and you could only swing from "webbing points."
What do want him to do? Redownload 100GB worth of mods at some point in the future in which he wants to play the game again?
I don't know about you but I'm keeping my 400GB modded FO4, even if I haven't touched the game in more than half a year. I rather spend 4 hours updating mods than spend 8 hours redownloading everything and spend another 8 hours debugging the crashes.