There are ways to add more but not to what OSRS Gold extent. The majority of the items you suggested would have no chance of having be effective. Nearly everything you mentioned at the beginning will speed up kills . However, many kills are almost over. Infinite auras has already become available to those who are pvming a lot. the refresh of their auras. Clue steps, sure, but to what purpose? A amazing reward that I can showcase for a couple of weeks , and then it's gone for ever. There aren't many things from clues that could be useful unlocks making them not very important to be doing.
I'm not saying there aren't things that could be added. What I am saying is the reason leagues were fun was the impact that change made to the way you engage in the game. Auto banking was awesome for OSRs as it's not the norm, and porters have been around for a while and we're familiar with that. Sure, there are endless options for them, but it doesn't feel new or feel like it's changing the meta since it's already a thing.
The last recall was game-changing since it lets you skip the gw kc, and then return to boss. These are two things that we already have within the game. The combat auras slowed bosses down to 5 or 6 hit kills that is what we have. It's hard to imagine there being enough of a distinction to be able to appeal to the players that leagues have on osrs.
Naturally, they're "maxed out" but only in the base game. It's like saying "who really cares about the pvming of leagues, you already get speed kill successes in main game"
Leagues are comically fast for example, the vorkath speed kills using knives' edge and dharoks. That's part of the appeal. Auras do come with "infinite" resets once you bank MoW/Reapers, but when certain auras remain in play, then it permits players to have multiple auras running at the same while opening up new possibilities for the "comically powerful" aspect to stand out and players to have fun.
Clues have a use, since forts are a bottleneck for items such as alch-onyx or hydronic.
It's more than just auto banking, it's automatic processing, multiple gathering, and so on. Sure some elite outfits or arch relics have the ability to perform that 100% or proc chance, but that's beside the issue. Now it's 0-time as there is no need to gather or make porters, and you get it alongside other benefits.
The Last Recall has more uses than just combat. Questing, skill and general game play all benefit from its active nature, so much so that it was selected 90 percent+ in Trailblazer as well as QoL's infinite runs twist, which is the reason they're always re-occurring. Yes, leagues may not be accessible to all. There's more "set up" before buy old rs gold the fun in RS3 and OSRS due to factors like invention, arch, etc.