My source of confusion is that if you ask a player to "Roll an INT check" or "Make a STR check" or any of the others, the maximum add to their roll—buffs notwithstanding—is generally going to be +5. I find this a little limiting when we consider suggested DC and the bonuses from skill proficiencies. So, a couple of things:

• First, a level 1 character with a +3 mod and proficiency can match a +5 Ability Score without taking two ASIs. So, the barrier to higher rolls is lower.
• Second, if we're advised that a Medium DC is 15, then adding skill proficiency (or, gasp, expertise) helps immensely increase the odds to meet or surpass that threshold. Someone with a +5 can meet that threshold, but the odds will always favor ability checks that include proficiency. Pure ability score checks will (well ok almost!) never pass very difficult or nearly impossible DCs.

Any thoughts? Am I overthinking this? Having trouble finding out if others think this is an issue or if there's any input on this, so here are the main questions bouncing around my mind—and any and all thoughts are appreciated:

• Do, or should, you use a modified DC scale for pure ability score checks? Or should you always try to pair an ability score check to a skill?
• When you call for an ability score check, do you allow players to advocate for using particular skills?

I personally rarely use pure ability checks, and when I do I usually let players add proficiency bonus if it makes sense. (A barbarian could add proficiency to strength, a wizard could for intelligence, ect)

If you want to use them and go with the RAW, I'd actually keep the DCs. If the DCs are easier, your basically giving proficiency in it to all the PCs, and therefore reducing the value of skill proficiency.

That's a really good point about avoiding devaluing skill proficiency that I hadn't thought of. Thanks!

Quote from Weylin_Brambles >>

the maximum add to their roll—buffs notwithstanding—is generally going to be +5. I find this a little limiting when we consider suggested DC and the bonuses from skill proficiencies.

It's not too bad. An untrained 20 STR character can succeed on a very hard task 1 in 20, and will never succeed on a nearly impossible task without external aid (bless, guidance, etc).

I will generally allow adding an appropriate skill or tool proficiency even if the test doesn't mention one, and traits such as Jack of Trades or items such as a luckstone always apply.

Most of the time I call for an Ability (Skill) check unless it doesn’t make sense. Then yes, I generally do knock the DC down a tiny wee bit, but only by 1-3 (half proficiency at their level.)

To be honest, I struggle to recall the last time I asked for an ability check that wasn't contested (in which case the suggested DCs are irrelevant) or where the DC was meaningful (determining success or failure, rather than how much time or other resources the attempt took). Straight ability checks are rare. 

Quote from Weylin_Brambles >>

• When you call for an ability score check, do you allow players to advocate for using particular skills?

 Pretty much always. As others have said, I very rarely do a straight ability check. If I did do them often, I'd probably let each class apply their proficiency bonus to the two abilities their main class gets save proficiencies in.