I agree with your general philosophy, but you go too hard into one side. Solo shuffle does help a bit, but I can see it yielding diminishing returns.
Let me give you an example. I have a prevoker alt and I’m hot garbage on it. I queued some structured 3s with my homies and they were just flopping.
I looked up cdew and some other r1s playing prevoker to see how they were pumping big numbers and doing the prevoker things and I realized what abilities I was supposed to be combining and when. It still doesn’t make much sense to me, but doing solo shuffle helps me get better acquainted with the kit and how I should be using things to go for CC.
You’re absolutely right that 3v3 is not the same as solo shuffle. Solo shuffle is way easier, from my limited and biased healer pov at least, in the sense that the lack of coordination from the enemy team gives me more room to breathe. However, due to the exact reason it is easier, it does provide an easier entry into 3v3.
Here is the TRUE truth about skill in PVP: