I ran it for a while on my ultra 24 until I just installed linux on it. But it was interesting dipping my toe in the solaris world

Still have a couple original Ubuntu CDs floating around the house after 2 subsequent moves.

I submit that the problem was Solaris 9 just being massively overtaken by desktop Linux in every way - easier to install, faster, simpler to patch, better GUI, more software available. Solaris 10 was too little too late; it already had to compete with mature Linux offerings that had a greater mindshare, and the excellent features like Zones were too far ahead of their time (and lacked the centralized store of downloadable Zone-prepackaged apps that is really the reason for Docker's success).

Purity doesn't matter in practice - especially in a world where OS installations are increasingly ephemeral and ideally immutable.

I always hear DTrace is awesome, but have never used it. And seem to have gotten by just fine... what am I actually missing?

ZFS, on the other hand, was so good that it has outlived Solaris itself and is at the core of e.g. TrueNAS as a commercial product.

Do you have any recommended references to understand that concept and how it plays out in Solaris?

I find myself in the middle of what I imagine are similar design challenges in software packaging, storage, integration, and deployment.

What does your setup look like? What kinds of workloads are you using it for?