okay so I'm pretty fucking stupid, but I'm not an idiot. Just launched this game for the first time in basically a year to test out that new smooth patch.

so last time my regular save, which is pretty light and regularly cleared out with the Save Cleaner tool, started taking longer and longer to load every time. It went from under a minute to 5+ minutes to half an hour in a handful of sessions. Thing is - I don't know why. I've looked at all the config files, I've had Task Manager and Process Monitor open while it's been loading. Resource Monitor to tell me what it's doing. And it makes no sense? I think these tools aren't even showing the TS3W.exe process properly, it's doing everything through the launcher and it's completely eating itself up trying to access game data. It's not telling me which data though. On the one occasion that I could see it accessing files in real time, it did so at like 5 bytes per second? I waited patiently for it to finish, and when it eventually did, it was a pain in the ass the whole time and then unceremoniously crashed.

I've long given up on this unplayable pile of crap. Whenever something new and clever comes along to make it run properly it works fine for a week, and then this absolute pile of garbage just finds another way to make itself even more unplayable. However as a man with an ego I also refuse to be outsmarted by a lowly 32-bit piece of software from the late 2000s. I don't care what kind of dark hackerman magic I have to learn to fix this shit, I'll do it.

also whenever the game process is running, it's pretty much constantly maxing out my GPU? Talk about an overinflated sense of self-importance. if it can eat up all my system resources why doesn't it do it in a way that's HELPFUL? good god.

how's this - different save. Same world. Bigger Builder's Island or whatever. Just loaded in, took about 10 seconds. NOW IT'S WORKING. Conventional human logic would lead me to believe there's a problem with my save, then. Bad CC maybe? this one has 2 lots and 8 Sims in it, the other one has a couple of dozen and about 150. I know TS3 hates me with a passion but I know it well enough to have questions about this behaviour.

Since you've mentioned maxing out the GPU, I have to ask if you've capped the game's frame rate. That's one of the critical fixes on modern hardware and the game should not be run without it, especially on powerful GPUs. Along with that, it can be useful to update the game's Graphics Rules/Cards files to increase texture memory and recognize the card.
Although these two are more graphics-related, I did notice some improvement in loading times after doing them (perhaps capping the FPS helped?).
As you've mentioned, bad CC could be another reason, but at least that can be tested easily; just test in a fresh Sims 3 folder and see what happens.

So how do I identify bad CC? Sims3Dashboard isn't showing any. Do I have to sit here and analyze the loading process in realtime with another piece of external software? swear to god

You do it the old fashioned way? The 50/50 method. Take out half the cc - test in game, take out another 1/2, test again. You will eventually track it down.

oh yeah, good one. Why didn't I think of that myself?