Completely stopping co-op is something that's not going to happen for a long damn time. I use it primarily so I can get a feel for what the champ's talents actually do, as well as an initial test for item builds -- to figure out roughly how the progression works and what to loosely expect from performance. In the poppy case, I now have a better idea of exactly what a few items do for her skills and how those skills react to certain situations, and am now much better equipped to apply it to a more skilled opponent. Better to do one low skill game to ease in than three or four higher ones that just demolish me, just to get a handle on exactly what the one let me figure out.
I do alright theory crafting a lot of that, but without some actual hands-on in a fairly loose situation, when I try to apply it to a more capable opponent, I just melt -- and worse, I don't really learn much from it, because I don't end up able to actually lever the setup's capabilities in any way, because I'm too busy having no real hint what I'm doing and what certain things are going to do, and getting squished into the ground because of it.
The last time I went into a PvP with a build I hadn't ran through co-op first, I ended up 1/6 and just had no flipping idea how to actually work what I was trying to work. The only thing I learned from it was that laning against malph with Mundo is somewhat suboptimal, especially in the early game.
To put it another way, I'm not nearly at the point where I get much out of blind runs. Start small, work up, works better, for me, for now.
E: Honestly, it's very similar to how I've played most roguelikes. Do it on easy or cheat to ease the game first, to learn the system and how certain situations play out, then come through and play it legit. It saves so much damn time for me it's ridiculous.