I'm also a LR classic user. I think it's pretty terrible by certain aspects, but I haven't found anything better. No idea why the UI lags on a pretty high-end machine, even with test catalogs. And I'm talking about scrolling, or showing and hiding panels. Plus, the worst offender is making me use Windows (on this point, only Darktable is better – no, I won't buy a mac, it's way too expensive for my needs).

Price-wise, it's kinda expensive, but the buy-it-for-life alternatives aren't exactly cheap, either. You should hold off updating for multiple years to save money compared to the LR subscription.

Now, I haven't used the alternatives for more than just a short test-drive, but the recent improvements in LRc would have made me upgrade anyway. I'm thinking specifically about the noise reduction you mentioned, but there's also all the object detection in masking which saves a ton of time, and the ai object removal which is pretty great when I need it – saves time compared to fiddling with the old healing brush.

I think the alternatives have also gained similar features recently, which would have likely required a new (expensive!) purchase. But, I guess if you figure we've reached some kind of plateau and don't expect to have a new camera in the next 3-4 years, going for Capture One or similar may be a better bang for your buck.