Modern subsites?

I'd rather not have to sacrifice information architecture and usability for the sake of performance, especially in an Intranet as its main function is to provide information. So my concern is more whether we are losing an aspect of information architecture that can be beneficial for certain types of users, those that prefer browsing to searching.

At least one scenario we use is a site collection of clients.  Each client is a subsite which in turn has subsites for those projects.  We could have a hub that surfaced the site collections of clients, but then what about the projects and searching across all of that structure?

I'm glad you qualified the multiple List/Library approach for small segregations.  I've seen the opposite, and the job of trying to split that information apart into separate sites is quite a bit more difficult than moving a subsite into its own site collection.

But that said, we haven't had a lot of people "with a love of subsites" chiming in :-).  And maybe I just need to get my head to think a different way.