Why is forming the HRE the fail?
You loose out on 2 dip relations, all the nifty free vassals, have to do all the micro management war fighting yourself (horribly tedious and not fun), and the aformentioned diprep.
Diprep is only important for france atm... Once I can finally vassalize that fool, I can revoke the privilage and vassalize the remainder of the non monarchist HRE states. Russia has hit 90 tax base, even with me growing (and building) Currently sitting on 2000 tax base myself. The -100 can never be overcome for vassalizing him. Coupled with this current 14 year regency. This will not be a 100% WC.
My plan has been so far, to abuse alliance webs to get wars against those who are in a coalition. Without fighting that coalition. Not one single coalition war has happened, and some people really really hate me.
That plan requires constant little wars to be effective. Now... I will be looking at one mammoth war to catch up in time. Which will likely put me in the position where NOONE will not be in the coalition... Uhhhg.