What does 'gaming time' have to do with long rests? There is no rule in the DMG that says people get a long rest at the end of a session
There isn’t. But (for instance) travelling 1 week from a city to a different city, you may have several one-encounter days. You definitely aren’t going to have 10-encounter days getting from Waterdeep to Bryn Shandar or your players are going to get impatient.
Likewise on a single day in the city. The DM might through in a combat or other encounter to spice things up, but they aren’t going to throw in 6 encounters without slowing everything down to a crawl.
Invisibility, polymorph, dimension door, skill empowerment, spider climb, find the path, pass without a trace, glibness, fabricate, tongues, comprehend languages etc.
I mean pretty much every spell that can be cast out of combat allows a spellcaster to contribute outside of combat.
And explain how they're both more useful than say a Rogue with reliable talent and expertise in Persuasion and Insight, even before you get to the problem casting a spell in front of the King, an important NPC or any other social encounter might cause.
There are definitely some social encounters you could try to sway by using enchantment magic (and if you are a subtle sorcerer, you don’t even need to worry about the social ramifications of doing so), but there is a much wider array of both social and non-social non-combat encounters that can be resolved by magic, often exclusively so.
For instance, a character or NPC that fails their save against mummy rot.
But those abilities to shine out of combat generally use the same resources used to shine in combat. If you want to Charm an NPC, Teleport to the Dungeon, and Fly up a wall, you're burning resources that are needed in the combat encounters for that day.
Riding a horse, using Persuasion and climbing a rope are all just as effective and dont use resources at all.
That depends. At higher levels, spellcasters have so many resources (and many low level spells continue to be useful at higher levels), that burning resources is not a concern. Not forgetting that a lot of useful out of combat spells are rituals and therefore do not burn resources.
At low- and mid- level, you have a point. Of course, spellcasters get to choose
where they get to be effective (which isn’t the case for non-spellcasters), and even if they choose to be effective outside of combat, they still remain reason effective
in combat, due to cantrips.
That's not my reading of the downtime rules.
Many of the most effective things spellcasters can accomplish during downtime are not mentioned in the downtime rules.
If a DM wants to implement stupid houserules to punish martials, and not police the AD, then of course they're gonna suck.
I think you are overestimating how easy it is to police the adventuring day, particularly if you are aiming for a default of 6 encounters, 2 short rests.
The point that I always come back to is that this is extra work for the DM.
I absolutely take great pains to ensure that spellcasters don’t overshadow martials, including liberal use of doom clocks. But it is extra thankless work.
And guess what, in large parties, with lots of casters, 6 encounters isn’t enough, since each caster can take time to shine, leaving non-casters with very little opportunity to distinguish thrmselves.
Only if he lets it happen. If the PC wizard exists, then those spells are known and countered for. Enemy troops have a wizard of their own for example, and soldiers know to wake up comrades affected by the spell.
Works less well for the many fantastic monsters the DM may want to use.
Again; this is the fault of the DM - not a fault of the rules.
I think it is an easy out to blame the DM for not doing extra work to restrict casters by having enemies counter spells and adding additional encounters.
I think that even having the balance point for classes be 4 encounters with 1 short rest would greatly diminish the complaints of martial-caster disparity.