Fanaelialae
Legend
Compare those feats to other feats or published official 5E adventures. If a DM has to work hard to accommodate these feats or target rare saves with illithids it might kind of prove my point.
Catching up on this thread and this caught my eye.
Why would you assume that the DM wouldn't have to work hard to accommodate optimized characters, much less an optimized party designed for optimal synergy?
As far as I can tell, the base game (and official adventures) seems to be designed so as to be approachable for casual players. It doesn't assume optimized characters, much less an entirely optimized party.
Due to this, a DM needs to take optimization into consideration, much as if they were to give a Staff of the Magi to a level 1 character. The alternative is to accept that the encounters will simply be that much easier. Fortunately, optimization usually comes with experience, and experienced players will tend to have an experienced DM who understands how to adjust difficulty to compensate for characters that are above the baseline.
As an example, consider that thanks to concentration and the hide action I think it's fairly reasonable to say that Invisibility is not broken in 5e. However, the players could create a party completely composed of characters that can cast invisibility, and suddenly the 2nd level spell enables the party to completely ignore a large variety (perhaps even the majority) of encounters. With 2 levels of rogue (for cunning action and expertise stealth) or sorcerer (for quicken spell) they don't even need to have the spell cast beforehand, because either of those classes enables you to hide during the same turn you cast invisibility. If some of the characters have less than stellar stealth scores, the druid could cast Pass Without Trace and assume an extremely innocuous form, such as that of a mouse or a fly. The DM of this party might say that invisibility is broken, since he needs to put in extra work to challenge the party. After all, what other 2nd level spell enables the PCs to treat most encounters as if they weren't even there? Certainly, the WotC modules aren't designed for challenging a stealth party, so such a party might breeze through such adventures. Now, I'll grant you that this party might miss out on leveling if the DM doesn't award xp for the encounters they bypassed, but even if they fight they can cherry pick which encounters to engage with and do it on their own terms (likely with a surprise round). From this DM's standpoint the invisibility spell might seem broken, but that doesn't actually mean it's broken. It's simply that the players managed to create their party in such a way as to get the most bang for their buck.
The DM could simply ask the players not to optimize the party like this. After all, if the DM increases the difficulty of the campaign to compensate for their optimizations (making every encounter deadly x 5) things may simply escalate to the point of mutually assured destruction, which isn't likely to be fun for anyone involved. Another option is for the DM to simply do his best to challenge the PCs without making every encounter a TPK waiting to happen, but that will generally involve more work for the DM. Finally, the DM might choose to do neither, keep the game at baseline difficulty, and let the players breeze through. Either the players will enjoy their power trip, in which case at least the goal of fun (for the players) has been achieved, else they'll grow bored of it and next time hopefully create a party that can more reasonably be challenged by the base game.