The problem has to do with the capped tomestones coming from dungeons. Because tomestone armor is always higher item level than dungeon armor, the tomestones become the true reward from the dungeon - not whatever you find in the treasure chest at the end. This problem actually got worse with Heavensward, because you can purchase raid-level weapons (ilvl200) without raid drops. The lack of a drop requirement (Unidentified Allagan Tomestone, etc) completely nullified Ravana and Bismark weapons.
The solution, I think, is to rework how tomestones are distributed and what they can buy. First of all, raid level gear should require raiding - whether it's 8 man or 24 man. Secondly, dungeon gear should be a viable entry point to raids. Primal drops should fill the gap along with crafted gear. I think a decent drop setup would look something like
Patch 4.0 hits!
Non-expert dungeons drop their old gear and uncapped tomestones that can be used on crafting materials and gear that prepares you for current experts.
Expert Dungeons should be a bit more difficult than they are now. They drop item level X armor and (weekly capped) dungeon tomestones that can be used to purchase item level X items. Tomestones are meant to mitigate bad RNG and you should be able to cap them after 3-4 runs.
Crafters create tokens that can upgrade Expert Dungeon and Expert Tomestone drops to item level X+10. They use materials from tomestones, drops, and gatherers.
Primals drop item level X+10 weapons and accessories.
8-man raids drop item level X+30 gear and (weekly capped) raid tomestones that can be used to purchase item level X+20 gear. They also drop upgrade materials that turn your raid tomestone gear into X+30. Defeating half of the raid is enough to cap you each week.
Then, patch 4.1 hits
New expert dungeons drop item level X+10 gear and (capped) dungeon tomestones that let you buy X+10
New primal drops item level X+20 weapons
24 man raid drops item level X+20 gear (1/week) that can be upgraded with materials from the 8 man raid to X+30. You can earn raid tomestones from this once per week as well (weekly quest or something), equivalent to defeating half of the 8 man raid.
By doing this I think it'd smooth out the curve a lot. Unfortunately you're left with the problem of "without raid tomestones why should I keep logging in every week?" Really, they just have to create more raid stuff. With more bosses they can make it easier to pug/get into raiding.
It's pretty stupid how right now you just skip every piece of old content entirely. It also leads to a lot of dead on arrival content like Void Ark. No one is doing that shit for the gear - only the upgrade items.