You're comparing density-focused server die to client-only something. Your suggested bump is too small for AMD to waste time and money that could be put into making Zen2 better.
Since 12LP delivers ~10% more performance with 7.5T HD libs, they might as well sacrifice desnity and go for 9T HP/UHP ones.
They will also optimize for clocks, because why not?
Basically they will try everything to delete Intel's clock advantage.
I think you are over focusing on this as AMD putting in a lot of work. They started on a LPP process for several reasons including EPYC. They always had plans on letting Ryzen get a bump for a new model this year by moving to LP. I don't think they ever had dreams about really taking it to Intel in 2018. 2018 by all accounts seems to be about treading water till 7nm, where they would be in position to really put the screws to Intel in lots of ways. The move to 12nm has more to with GF basically saying that you wait a couple more months and we will have something better and it won't take much work from you. That's the only reason for that move. Not because AMD is tossing money at the pure idea of using this process change to assume a leadership role.
2017 Return to competitiveness
2018 Maintain competitiveness
2019 Use die shrink to assume performance lead.
There is a reason it's called Zen+
There is a reason why AMD called Pinnacle Ridge, Summit Ridge architecture with "performance uplift"
There is a reason why AMD hasn't been all over the place talking about the switch to 12nm. Because it isn't real node shrink.
I think it's really important to understand that AMD is probably going to be in a good spot in 2018. They will close enough to Intel in clocks to not really matter. They can do some tweaks help eak out a little more IPC. In the worst case scenario Intel will have core parity with AMD. AMD will be able to maintain decent ASP even if they have to be a bit more of a value CPU than they spent 2017. But the full market availability next year of RR will make up for a drop in Ryzen value. AMD will get through 2018 better than 2017 probably. But that doesn't mean they will have the best chips ever.
Trying to make Pinnacle Ridge into something it's not. Is just going to feed into expectations. That are going to fall flat. Then it will be a disappointment. Then everyone will talk about how AMD screwed the pooch. AMD is better off making Zen 2 as amazing as we felt Zen was than trying to make up too much ground with Zen+. AMD can't do everything even if they wanted to and years ago they had to make a choice regarding what to do after Zen what to put the money into and Zen 2 is that answer not Zen+.