Hexblade warlock is powerful for the wrong reasons and warlock

[MeeposFire]

Use the Gritty rest variant rule in the DMG, or turn all short-rest abilities into long-rest ones by multiplying them by 3 and taking away the recharge on a short rest.

Or change how long it takes to get a short rest. For instance you could make your first short rest only takes 5 minutes, your second could take a still short but more noticeable 15 minutes (or choose the exact time that works for you) to achieve, and then all short rests after that take 1hr to compete. The fluffy idea of it is that it takes longer and longer to get your stamina back as you keep pushing yourself during the day but the 1st two rests are short enough that even in groups that do less encounters you should be able to get at least 1 SR and in most games 2 short rests with few problems which makes them compare more favorably to long rest classes while making the long term prospects to be similar to the RAW in terms of overall power of a short rest class.

Then the only games where a long rest class feels like it is really ahead are those that do one fight and then long rest which if common you will probably have problems with all sorts of things anyway.