On the light issue:
1) Sometimes when you are relying completely on darkvision, you are going to miss important stuff.
2) Sometimes, when you are relying completely on light cantrips, monsters will see you coming.
3) There is no way to know for certain which of those two scenarios is coming next.
I don’t understand what the problem is.
As near as I can tell, here's what's going on. Some DM's have gotten used to using darkness as a tool to surprise players and keep them on their toes. Light sources, to them, are a trade off- how many minutes of light do you have? What do you have to give up (shields, two handed weapons) to have it?
This has run right into players wanting magic-users to feel magical at all times, not fire off a
sleep spell and be reduced to throwing darts or flaming oil, as well as a general apathy towards the style of play that has you tracking ammo and rations.
WotC
claims that 5e is more friendly to the old school approach to gaming, but it doesn't take long to realize that's really lip service. Cantrips that are as effective as crossbows are available to most caster classes; they also don't require ammunition. Light is plentiful. Spells that provide food, water, and shelter are common.
Adventure guidelines lean into limited encounters between rests, there's lots of out of combat healing available if groups want to use it, and players have ample opportunities to "opt out" of parts of the game that they may not find enjoyable. In addition, these same guidelines tell us to award players with tons of money, so purchasing ammo, rations, or whatever is generally not a problem either, as long as you can carry the stuff. Anyone can learn to use Thieves' Tools, Feats exist that make finding traps and secret doors a snap.
Honestly, I'm actually surprised darkvision has a penalty at all, though many groups seem to ignore it entirely, and some are optimized to the point that the disadvantage doesn't even slow them down.* I mean, darkvision had no real disadvantages to speak of in 3e and 4e, and I don't remember that being a big problem either.
*Supposedly. When I run, and enforce the disadvantage, I've had players run into ambushes and traps enough to make them break out a light source, but I've had people claim this isn't a meaningful enough penalty.
The only way to force a certain style of play is to put your foot down and invoke optional rules- but to my mind, if the players really want to just hang out in their Leomund's Portable Bomb Shelter and eat Goodberries, why not let them? It's obvious they don't think getting lost in the wilderness and scrounging for edible grubs and tubers is any fun- if it was, then they wouldn't be using these options.
I mean, so what if the party isn't using light? Most monsters have ways to not need light either, so the way I see it, it's a wash. Granted, there are things like Drow, Warlocks, and Twilight Clerics that can give themselves a much longer range than 60', but that's not usually what the complaints are about- it's more that "too many" races have darkvision.