No, it changed. At no point did House of Splendor/Collectables turn ins dip in exp until DT came out and levels beyond 90 were an option. My level 88 CUL on an alt still gets full EXP from collectables from ARR, HW, etc. It's only once you get to level 90 that it drops, and it drops for ALL collectables except the level 91 ones. So any extra level 90 collectables might as well be discarded for how useful they are.

It's possible that the Dwarf and Namazu Society quests got nerfed when you hit level 80/70 respectively already. I'm pretty sure Namazu didn't because I was working on those for a while back during SHB, but it's been a few years since them so I can't say for certain - though I probably wouldn't have finished that quest line if it wasn't giving me exp in return. I also finished all the Dwarf quests before EW came out, so I'm not sure about those either. I don't like that the exp nerf dis-incentivizes players from actually completing those quest lines though, especially since those quests have a set limit per day anyway.

It's one thing to encourage players to move on to the next expansion's crafting and gathering, but they should be dissuading people from doing SHB and below content when you get to DT, not EW stuff when you literally JUST got to the first level for DT (and technically the *last* level of EW).