"Cant see and automatically fails any ability check that requires sight."Okay. No, you should read all my remarks as limited to mechanical effects (actually imposed by the rules).
A foe you can't see still makes noise. Unless it actively stealths - paying the game costs for that, and beating your passive Perception - it does not gain any of the benefits you give.
An invisible Wizard can still be targeted. In fact, everything is the same except what Invisible the condition tells you is different.
Meaning you can move alright in outdoorsy darkness, even though darkness penalties apply.
What sight-based checks tell me is you don't get to apply sight-based bonuses. It doesn't mean your Speed is affected, because it does not change your Speed, for instance. If the rules meant to hobble your Speed, it would have said so.
It is in that light ([emoji3]) you should interprete me when I say rulebook moonlight is reasonable. And probably a lot of other posters in this thread as well.
Only if you assume everyone else is running Stealth as you do is there reason to find them unreasonable for not hating rulebook moonlight as much as you do [emoji6]
There simply is no common ground as regards Stealth and therefore illumination. Not in 5E anyhow.
Cheers
That seems to cover more than just bonuses - like say passive perception checks based on sight.
But one major impact is on all the various spells, feats and actions that require sight... Opportunity atracks for one, counterspell for another (but there are lots of spells - most of the non-aoe non-to-hit ones like hold person) easy to walk into a pit or snare that you would see normally etc.
This all seems to add up to a **lot** more impact than just the advantsge/disadvantage on to-hit - especialky when one comes from a pov of characters (p or np) working to exploit and utilize that huge advantage that opens up 8-12 hours a day.