Harper has a long enough track record to suggest "he is what he is", there's no upward trajectory.
Sure, there's always the possibility that the light could go on, but he's had a long time for pitchers to adjust to him and him to adjust back, whereas someone like Rhys has barely one ML season under his belt and that game of adjustment and counter adjustment is still progressing.
I think the rebuild got ahead of schedule, some young players were exposed as still developing, especially the three young SPs, but it's not time to panic, I always thought 2020 was the target date, and nothing this season changes that assessment. And as we saw, free agents can't do much to accelerate a rebuilding timetable, you arrive when your young talent arrives. Franco showed real progress, Altherr and Herrera regressed, Rhys emerged, Kingery and Crawford struggled, SD flashed then crashed, and so on. Arrieta, Santana, Neshak and Hunter barely moved the needle, even though all had decent seasons.
I'd extend Ramos, keep Santana one more year but use him less (but he showed a decent glove at 3B) and dump the rest of the TDL pickups. Build up the depth at Lehigh and Reading next year and let the young prospects take their lumps. This team should have a great pitching staff in a year or two, they just need to field a solid group of 8, and they're not far from it. Average offense, plus defense and top pitching is more than enough for a contender.
2020 projected lineup
C: Ramos (Alfaro, Grullon)
1B: Rhys
2B: Kingery
SS: Crawford
3B: Franco
LF: Williams
CF: Quinn/Herrera
RF: Haseley/Pujols/Cozens
Now if I can add a young FA like Harper at a reasonable (i.e. not gross overpay) I'll do it, but I'm not breaking the bank to upgrade with 30+ FAs, we saw how little that helped for the most part after the TDL. The real difference makers are usually home grown or obtained in mega-trades.