Bladesinger is a particularly problematic example, since that subclass grants something like 70+% of the capabilities of the fighter class, whereas the equivalent fighter subclass only grants perhaps 20% of the capabilities of the wizard class.
Bladesinger is an example of an issue where for some reason someone decided giving more to wizards was important. Personally, I think it's okay to have difference levels of combat vs magic in gish-type classes/subclasses but the wizard, a class so obviously focused on magic, is the last class I would consider giving that much martial capability too.
IMO, EK could have been given a bit more and bladesingers have too much going for them. I would be tempted to make bladesinger a fighter subclass instead of a wizard, and remove EK, tbh.
Spellcasters are often better at ability checks than martials due to their primary ability scores having more available proficiencies. Do you determine results to an ability check differently based on who rolled it?
In what context, however? STR and DEX are more useful out of combat than INT, WIS, or CHA depending on what is going on. My character cannot persuade a stuck door open or investigate across an open pit or crevasse. Spell casters may or may not have spells to deal with those but the ability checks aren't in their favor, and using a spell in that way removes the option to later use that spell slot again at another time to create an opportunity cost.
And look at monks or rangers. For all the complaints people might have both classes still focus on DEX and WIS. That's not just a spell caster thing. Rogues can focus on DEX and pretty much any other ability score they want. Reliable talent with some WIS and CHA on a rogue and proficiencies goes a long way in this area.
We aren't even talking about all spell casters in a general statement about primary ability score. INT is only there for recalling lore and investigation. It's not helping much in social or exploration challenges at all. WIS is useful in some ways but it's not going to accomplish CHA challenges either, and monks or rangers are going to use those stats too. CHA is there for bards, sorcerers, warlocks, or paladins. Useful for a few social checks but not other checks.
I don't think there's any catch-all advantage in the spell caster casting ability score that really outshines the number of uses for STR or DEX in exploration. My question would be "how is the DM populating challenges in the adventure"?
OK. But presumably that Warlock has their own backgrounds, interests, general world knowledge and skill modifiers, and you grant them the same benefits when investigating an aspect of the world where those are relevant? If you determine a check is needed and neither (or both) characters have relevant benefits from the above, do both characters have the same DC, and both get the same results from rolling the same total?
I would answer that it depends on context and circumstances. A DC 15 climb check is a DC 15 climb check. A persuasion check varies in results depending on factors such as friendly/neutral/hostile for whatever reason.
There's also the repeat roll rules and spending time to succeed if it's possible to succeed in the first place. Someone with a +3 ability score and +2 proficiency bonus and time can auto-succeed on DC 25 checks at 1st level without the pressure of danger. Spells that also apply ability checks cannot do that because an action doesn't allow for the time component within that action.
That's one of the benefits in how I play bards. I don't uses a spell at all when a skill can do the trick because spells are a finite resource and skills are not. Why would anyone spend a finite resource unnecessarily? Using those skills instead allows for having those slots available for when they are needed. IME, using spells outside of combat for utility is often only something that is done as a backup because of that resource management component, and typically only when a time crunch is on. That makes it an uncommon shine moment when it does occur.
This is a really cool way to handle those sort of interactions, but at the end of the day, if the ability checks fail and the NPC won't tell the party the information that they need, the warlock may have the option of casting suggestion, or scrying etc. The fighter does not.
At its core, this is one of the greatest misapprehensions of this particular issue: the fighter class doesn't get creativity, roleplaying, ability checks, and background features to make up for no spells compared to spellcasters. The spellcasters get all of those things as well as spells.
This is true, but those spells are shine moments. The fighters get their shine moments in combat or outside of combat on STR or DEX checks, which happen often enough. And any time the spell caster casts a spell that slot is gone for later. Running low on or out of spell slots increases those moments where martials have more opportunity to shine.
I mean, in a full Adventure Day the casters will be running out of Slots handily.
I don't necessarily let my players know how long they might be adventuring in the day. DM's have agency in determine appropriate or available times for rests. If the players don't know how long the adventuring day is going to be they become less likely to use those spell slots and may end up with slots at the end of the day or out of slots before the end of the day. I vary it up to keep players on their toes.
The fact that they automatically replenish after a sleep is exactly why it’s a waste not to use them all before sleeping. If they didn’t come back after you slept, it would be best to hold onto them as long as you can. Since they do though, sleeping while you still have unspent spell slots means you’re effectively recovering fewer spent slots than you could have done.
That assumes the spell caster has something applicable to which the spell slot can be applied. Ideally the slots should have been spent before that point but spell slots remaining right before a long rest can go to waste if there isn't some applicable way to apply them.
