I actually doubt that there is or will be a definitive "end" for the game as many events and contests also revolve around upgrading and leveling guys so eventually even the oldest veteran players would need new guys because they already fully upgraded and leveled everyone available in their harem.
The extensive filter options are there for a reason after all, although I do agree that reducing the amount of new guys introduced in quick succession would be preferable with more chances to get guys you missed elsewhere.
However, when I look at how often those monthly mega events pop up now which each time introducing four new 5-Star Legendary guys + Legendary Days + Legendary Contest + Mythic Days + Path of Valor + Path of Glory + Path of Attraction + Boss Bang/Double Penetration there are still lots of new guys coming, but the focus shifted heavily towards time-limited events rather than permanent game features such as Places of Power (PoP), Club Champions, the permanent Pachinkos (which do get the new guys every month from classic event) or the League.
The only non-time limited feature which still regularly receives new guys is the season, as story progress in the main adventure is also rather slow.
Another shift also happened in the vein that stronger guys like 5-Star Legendarys become evermore numerous (I have more than 130 of them already) and while Mythics remain the "crown jewels" guys of other Raritys like Common, Rare and Epic have almost no use anymore except when fitting Blessings occur or when you need more power in PoPs.
Rare 5-Star guys start to appear in later story worlds, yet for Epic there still exist only two (2) guys who have 5 stars.
1-Star guys are meant to help beginning players to fill out their harem and aid in cash income as well as with early PoPs. I think there exist enough of them for these purposes with 65, as for mid- and high-leveled players they serve close to no purpose anymore.