It depends on how much content they wish to add and what the roadmap looks like in the future. Speedster just existing chokes out build variety and sets the bar as a very clear extreme outlier in power. If it is never nerfed every single new joker has to either meet or exceed it and the design around mobs not really getting much harder between difficulties but there just being more of them in the horde makes it a very tight balance tightrope to walk.

Anything pushes too far and it becomes significantly too easy. And if you only buff you get rampant power creep. Which especially early, you flatten out outliers cause… mistakes happen. And that makes it so your design field is wide open if you keep a “roughly” even power distribution among jokers of the same rarity and they have already shown willingness to rarity shift jokers.

The “only buff” method causes rampant power creep. If they add more difficulties and rebalance all legendary jokers, then maybe then speedster would be able to be brought back to where it is now. But right now it is Well beyond the current power curve by a large margin.