Just because you and some other players envision the system this way doesn't mean that SE or all players do.
From comments I read and hear, most seem to see relics as something to collect to kill time between content releases and collectors tend to want it all. That means that someone newer to the game likely isn't going to want to be restricted to just the current expansion relic for one job. They're going to want all the relics from each expansion for each of the jobs they play.
That becomes a daunting task as new relics are added each expansion unless the process to gain those relics gets simplified over time. And so that appears to be what SE is doing. It's annoying to those who have been playing the game since ARR and have built their collections as each expansion happens. They now have less to fill their time. It's a blessing to players who are newer to the game and excited to have the chance to collect all the "cool things" that some MMOs remove access to after a certain period of time.
A game striving for longevity has to design for the latter type of player, not the former. Otherwise they only lose players while gaining few new players because new players feel like they'll never be able to get all the rewards that helped attract them to the game.
If it's a long grind that's meaningful to you and not having the weapon itself, then switch to the long grinds in the game that you haven't completed yet. Extremely few, if any, players have done them all. If the content for those grinds don't appeal to you, then you may want to find other games that have ones that do appeal so you can play those games once you've consumed what content that interests you in FFXIV (or vice versa).
But I do not see SE continuing to create long grinds for items that have new versions added every expansion when a large part of the player base has barely had the opportunity to start building their own collections. It would be a bad business decision.