Yeah it's definitely a very fragile platform, and it has some serious issues that manifest in large and/or long running projects that have been worked on across successive updates. I've definitely pissed some people off by talking openly about these problems, primarily because they never experienced them in their projects and didn't like anyone tainting their view of Sonar as the "best DAW in history, ever."
I honestly think it's probably a great DAW for working with traditional band recording setups, and I get the feeling that's what the vast majority of users do with it. Someone asked the question on the Facebook group a while ago, "how many tracks do you typically have in a session," and a lot of people answered. The average seemed to be in the region of 10-30 tracks with most people saying "just the usual stuff - guitar, drums, bass, maybe a drum VST and a synth pad." Sonar handles that pretty well. Here's one of mine zoomed out, as you can see there is a lot of stuff going on (this is with all of the MIDI tracks hidden except a handful), about 20 minutes worth of timeline.
I've noticed as a rule of thumb that when I start to get irritated by the length of time it takes Sonar to save a project (i.e. there's no quick CTRL-S and continue with what you were doing, you have to sit back and wait a while), that's about when the project starts to become troublesome. It's not exactly as if it's taxing my CPU too much either - I mean each of these tracks have upwards of 5 or 6 plugins on them (maybe more), but my CPU meters are showing just over 50% (mind you, with maximum buffer size). But really, in the realm of electronica, this kind of project size is typical. It's not as if all the tracks are playing at once, there's just a lot of sounds throughout the project. I'm convinced that it's when you have a lot of MIDI and automation flying around, that's when Sonar starts getting confused and sending signals where they shouldn't be.