I did live in a world without FP, but I don't remember it very well, but what I do remember is practically empty parks, so FP was hardly necessary. We also didn't know how to maximize it's use when I was a teenager after it was initiated.
On our last trip, I don't think we ended up waiting more than 15 minutes for anything. Now it seems that even during less crowded times, most of the popular attractions are starting out with waits of 20 minutes or higher. If I don't manage to snag a SDMT reservation in the next week (I want it done before the 30 day window opens for the GP) then I'll either have to switch days entirely, which would cause a domino effect with all of my reservations, or I have to make it to Rope Drop as early as possible to be as close to the front of the pack as possible, which means waiting 45 minutes outside the park, then a while on the inside. Or just waiting anywhere from 30 minutes to an hour whenever I make it into the park, which may be a more likely scenario with a rope drop reluctant spouse.
I don't know how tiering might work at the Magic Kingdom. I'm sure they've done trials, but it just seems ridiculous to me that two attractions who have posted waits of well over an hour part of the day, even during 'slow' times would be free game for FP for whomever happens to try to reserve them first.
(I did just manage to get a Mine Train reservation, so that makes me happy, but it's during a time when I wasn't planning on being in the park anymore, because DH needs a break every day. I may just have to keep DS with me, and make DH take DD with him back to the hotel. That's probably a better option that trying to Rope Drop it, even if it's not perfect"