I've been saying this exact thing for years now. Having one of the most important Ultima items only be available a month out of year, with that month being the busiest month of the year, is just a bad idea. It's a large reason why I made the switch to Ephinea myself.
Being able to pay directly for hit/end game items probably killed the game as well. It was always slightly annoying to see somehow who joined 2 weeks ago decked out as much as someone who'd been playing for 2 years. PGF/Dark Weapon prices got so ridiculous around mid 2016 and stayed that way, to the point where if you weren't rich, you'd have to spend many, many hours just to get 1. Then assuming you didn't get all the Dark Weapons you wanted, you'd have to wait another year just to spend a lot more hours doing the same hunt during the busiest time of the year. Same thing applies to STA, which has about the same time sink required. I think everyone can kinda guess that DTs won't go away, since without donations this server would've probably died out a long time ago, but it totally needs a rework.
PSO in general has a retention problem, probably do to the fact that the end game is just doing the same areas you've been doing but harder for gear. There's definitely things that can be done to increase the longevity of the player, though.
I do have to agree with this. Hucast having access to something like STARs Needle or DM Storm would be absolutely game breaking, Why play ranger when you can sit in the corner on hucast and 1 combo mobs with DM spam, while also having access still to DF.