Echo Bosses:
Echo Grotesque Guardians - The fight isn't meant to be the exact same as the regular fight, but putting that aside:
Dusk hits way too hard and hits through prayer (melees 35s through prayer and his ranged attacks on final phase hurt too)
A simple fix would be to let both be able to be hit by any style if you don't want to re-program the whole fight to be like osrs' echo gg fight
The gloves are nerfed and don't boost barrows set effects anyway so I think the above should be a nice compromise (was this also a design choice or was it left out?)
Echo Hespori - Should have a guaranteed/pity drop system for Nature's Reprisal. I am 12kc without one and it takes around a full day to grow a hespori seed, since I didn't take Farmer's Fortune. It is an early game weapon and is quickly outclassed by ranged and mage weapons, and is only niche for melee.
Clue drops:
Clue drops on Alora roll on the primary drop table for some reason. If you take Treasure Seeker, your loot pool gets diluted so much by clue scroll boxes because they become 1/6. They should roll on a separate drop table. Eg I went 448 kc dry for Ultor Vestige on Vardorvis because he drops every single clue scroll tier, and went many kc dry for a Rancour on Araxxor.
Group content tasks:
Wintertodt is so dead beyond the first week or two unless theres an event on which happened twice from my knowledge, which was a D Axe/Phoenix pet event.
Zalcano is one of the worst bosses by OSRS design and could use many tweaks on Alora to make it actually fun and not impossible to get people together for/fun to solo. Eg Tephra not being destroyed between phases or rounds, substantially increased loot quantity.
Task Variety:
Easier said than done.
A good idea imo would be a some collection log slots tasks (300/400/500, it currently ends at 200), incentivises interacting with a lot of different areas of the game.
My biggest issue with some tasks was ridiculous kc amounts for some bosses. Eg 5k Lizardman Shamans (they respawn very slow), High kc group bosses that I mentioned above, 1250 Alchemical Hydra (if each kill takes 1 min including respawn time, thats over 21 hours for this task), 250 ToB, 250 Shayzien basic AND advanced laps.
Karamja also should have been a free region with how little tasks and points it gives vs the other regions.
500 of each clue casket grandmaster tasks is way too much.
Karamja/Donator zone:
Karamja should have been free
Felt horrible to be locked out of Shilo Village gem mining for opals/topaz/etc as a f2p. Move DZ somewhere else instead and let an integral part of the runescape map be accessible to everyone imo.
Controversial take: Disable donating on a Leagues account so the playing field is the same for everyone.
Relics:
Total recall should just be given to everyone at t4 or t5, maybe with a cooldown if needed. Bankers Note and Equil outclass it in every way.
Treasure Seeker - See above in Clue drops section. Still feels extremely underpowered compared to Arcane Selection or Farmer's Fortune. Lessen the amount of puzzle boxes you get or something as those are the main culprit in making clues feel so bad.
Equilibrium is quite strong as there are so many 25/50m exp skilling tasks and is a must pick for anyone wanting to compete point wise as those xp tasks are more "efficient" than the lengthy pvm/boss tasks.
Megarare Voucher pity:
I got lucky enough, but there's literally a guy with 339 CoX with no megarare 
. That's around 50 hours of only CoX if they take around 10 mins each on Leagues.
Either that, or make every HMT a guaranteed purple. CoX should be 1/4 (as it is on OSRS). ToA's guaranteed above 700 (OSRS).
Accessible items:
Rogues outfit, Magic secateurs, Ava's, Locator orb would have been nice to have been obtainable (some are impossible during Leagues due to vote point timegating).
Blessed sickle for Morytania diaries being locked behind vote points feels bad too.
Crystal crown being 500m is overkill probably unobtainable for most players even with trickster
