Making direct hit and crit chance % buffs increase the critical/direct hit damage done would only make specific jobs better than others (e. g. a 6.1 SAM would benefit a lot, whereas a job without guaranteed crits will benefit depending on their crit chance).
However, this is indeed a problem, and it has been highlighted before in the case of WAR in this thread (https://forum.square-enix.com/ffxiv/...eds-addressing).
Having guaranteed (direct) crit attacks is alright as long these anti-synergies between jobs are not created. It is also quite odd that DRG and DNC, for example, provide these kinds of buffs while having (direct) crit attacks of their own that must be used within them, or that WAR is the only tank almost unaffected by these buffs.
The suggestion I propose in my DRG feedback post for EW 6.08 (https://forum.square-enix.com/ffxiv/...-for-Endwalker) is to make direct hit/crit chance buffs increase the damage of automatic (direct) crit attacks and behave normally otherwise.
If we have Battle Litany up, and we use Life Surge on a Heavens' Thrust or a Leaden Fist Bootshine, the damage of the weaponskill will be buffed by 5%, with direct hit buffs working as usual. A direct crit attack under the effect of both Battle Litany and Battle Voice would be buffed by 5% twice.
Crit chance buffs would give a damage increase of half the chance, while direct hit buffs should provide one of 25% of the chance. Thus, a 10% crit buff like Chain Stratagem would increase the damage of automatic critical attacks by 5%, with a 20% direct hit buff like Battle Voice doing so by 5% for automatic direct hits.
A 5% damage buff for a limited time and number of attacks every 2 minutes (with the exception of The Wandeder's Minuet and Army's Paeon) should not be an issue, since it's a damage increase similar to other party buffs like Embolden or Trick Attack, with the only outlier being Devilment due to its nature as an individual boost to DNCs and their partners.
Making this change would benefit all jobs equally and avoid future homogenization issues in which the devs might feel that they have to change all buffs to flat % damage increase ones or remove (direct) crit attacks, which would make the jobs bland and uninteresting. Numbers could always be adjusted if needed to account for any potential tuning problems that might come up.
If they want to do things like avoiding huge damage variances while not creating anti-synergies between jobs, this should be the way to go.