My takeaway on F-16 SLEP was not "it won't be properly done," coming from guys I worked with who are far more knowledgable in that area than I am (and it's high on the priority list). Do you have first hand knowledge that says otherwise? I won't speak for Eagle/Strike SLEP, but it's not an entirely different animal. Of course any number of things (including SLEP) can be fucked up in the future by politicians, wayward GOs, some dickhead SES, etc., but its not really noteworthy in these types of discussions due to the universal application of fuckery to any program.
If you want to argue operation and sustainment costs (I probably understand them better than you think), then maybe you should be arguing why we're even using 4th gen fighters at all in the current wars. We've been destroying our jets for years doing shit a 4th gen fighter is way "over kill" for. Yet here we are, slogging away killing dudes on donkeys and dropping thousands of PGMs to move dirt a few feet. Do we need 4.5 gen fighters to take on those rolls? The reality is if something more peer-level kicks off, all that flying hour cost, etc. discussion would be fairly inconsequential when 75% of the Package AA/AB F-16s/F-15s didn't come home. How's generation for AC+ looking? Oh, and the CFACC objectives weren't accomplished either, so we'll have to re-roll a bunch of shit to future ATOs and DTs. Or there's the alternative of increasing capital in newer technology that outperforms anything that could come of a 4.5 gen fighter. It may not be cheap, but it's a lot cheaper than what the realized losses would be in the aforementioned example.