DND_Reborn
The High Aldwin
Ok, so tier 2. Proficiency is +3, even with maximum ability is +8... so still not even a 20 does it. They are at a point where a feat could double the proficiency bonus, so we'll go with that as well, making it +11. Now, they have a chance!I have the exact opposite problem, for me DC 30 is far too easy. Over multiple campaigns my players always find ways to jack up their checks around 5th or 6th level.
Guidance is +2 or 3 on average, a bard's inspiration (very limited uses) is +4 or 5, so together let's say +7 on average.
Now, you are up to +18. Give advantage and yes, you are at 70% (with expertise) or 50/50 (roughly, without expertise).
But, that assume a bard (with limited inspiration uses, granted short rest by that point) and guidance... oh, and the PC is no longer doing it alone...
Also, helping for advantage is not as easy as most people use it:
So, that means your PC "helping" also needs proficiency and maximum (or near it) ability and/or expertise to even have a chance. Otherwise, they can't help. If you have two such PCs in one group, with two PCs to do guidance (since it requires concentration) and/or a bard possibly expending two inspirations.
I don't know, IMO that is a LOT of ducks in a row. You mentioned your PCs are good at team-dynamics, but a lot of players aren't that well organized IME. I suppose if the DC comes up rarely, your group can handle it, but again a lot of PCs can't handle such tasks with even a decent chance of success.