@pglewis As of last night I'm finally at a point where, given an unlimited inspection time, I am averaging sub 60 with ZZ! It seems a lot of my gains are in consistency though, with my standard deviation dropping from 40s to 5-10s over the last week.
While I have no hope of doing inspection in under 15 seconds right now, I still try to go through it as fast as I can and have started using my fingers less to tag all the bad edges and instead only use them to visualize where the remaining bad edges are going to be after fixing the first four; this is a big step up for me and I think is largely why my times are growing more consistent. It's not longer about fixing six individual edges; it's about fixing a group of three then four, or fixing two then four or four then two - I've grown more versatile and comfortable with EO and for whatever reason fixing six edges is harder for me to plan than even 8 or more. I'm still not quite ready for EOLine and still do EO+Line, but I've start practicing tracking my line as I do EO as a "training wheel" until I can do full EOLine. Regardless, the time from picking up the cube and until F2L starts is about 15 seconds for me which is, honestly, embarrassing to admit. I think it takes me so long in part because I'm in the habit of checking for bad edges after fixing all of them - nothing seems to frustrate me more with a ZZ solve than discovering I missed a bad edge in the middle of a solve - and finding my first block or F2L pair can take a couple seconds. Then my LL takes between 4-7 seconds, depending if I know the PLL or not and if I need to U to recognize it.
With that in mind I've been memorizing more PLLs and have only the Ns left to memorize and only the Gs to finish cementing (just finished memorizing them yesterday). My plan being to get them all into memory then use a PLL trainer sporadically but frequently throughout the day, for a few days, to drill them and with focus on the ones I'm weaker with. I figure if I can reliably 2LLL in 3-4 seconds then it'll just come down to reducing EOLine to sub 5 seconds and I'll be sub 30 even without any real improvement to my F2L. From there my plan is just to practice strictly slow solving for a couple days at a time between Ao100s, with a focus on efficient block-building, look ahead and overall solve fluidity for a couple weeks; I'm hoping that will take me to sub 20 or sub 25. I figure it's at that point PLL will be more reflexive, I'll have an overall better understanding of the cube and learning to recognize and execute COLLs will be much easier; with PLLs to fall back on if I don't know the COLL yet.
I did try a handful of CFOP solves and set a new CFOP PB and Ao12: 39.03 PB and sub 50 Ao12.
It is interesting that I, as a newbie CFOPer switching to ZZ, improved at CFOP just as a byproduct of committing to ZZ. I suspect a big part of it is because planning my cross was ridiculously easier than it used to be so I was able to spot multiple options for my first F2L pair instead of being concerned with positioning the cross; and then as you said, the EO awareness really helps kind of organize things during F2L. I had my cross and first F2Ls pairs inserted, on average, in the time it normally takes me to EO+Line. My times probably could have gotten better with more solves because at first rotating was really throwing me off but towards the middle and end I identified it as a problem and simply paid more careful attention to it. I never learned OLL either but at this point it's very, very far down on my priority list since I would much rather memorize COLL. I still find solving with ZZ much more enjoyable and have zero regrets about switching to it.
But honestly, right now, sub 20 still feels like a pie-in-the-sky dream to me, like it probably did with you, with ZZ or CFOP. Even now my best ZZ time is 42.83 seconds and it felt like my EO+Line, ZZF2L and LL all flowed really well except a small pause on PLL. I take comfort in that when I watch sub 20, and to a lesser degree sub 10, solvers on YT I can mostly follow their turns and see what is going on if not where it's going and it wasn't but a few weeks ago I had to put things like that in half speed to be able to keep up. I'm hoping that with just time and practice everything will come together. I'm really not worried about getting my inspection time to under the 15s mark (well 12s mark) yet since I don't compete and speedsolve for fun more than anything else. I'm sure when I get closer to sub 30 I'll become more concerned with the, uh, legitimacy, of my speedsolves... but until then, I'm fine cheating my way to sub 30 with however much inspection time it takes me to build good habits LOL.
I've also been thinking of trying to learn to be y axis color neutral now, while I'm still slow, since I know I won't want to take the temporary hit to times if I ever decide to later when I'm faster and my habits are more established; but I'm not sure the best way to approach it. Would it be better to start with an adjacent to blue color (red or orange), or to start with the opposite color (green in my case)?