No, that's not at all what I'm saying.
I'm saying that for the most part creatures with resistances and immunities used to be a real concern, but is not that anymore. Sure there can be the odd exception, but mostly, you will have gotten the tools you need by the time you face that kind of monster.
Time and time again I read about a monster's resistance to magic weapons, or somesuch, but not even once has this actually shut down the party, forcing them into changing their tactics.
That certainly isn't my experience. We've just finished the Curse of Strahd AP, and we had to spend effort to ensure that we were able to fight some of the more resistant gribblies in there, even if it was just extra spell slots to enchant weapons. - We only started to find magical weapons at higher level -
after we had encountered werewolves and vampire spawn.
I would, however, make a distinction between shutting down the party and simply forcing a change of tactics/making things harder.
Sure, it has meant a fighter have had to use another weapon than his favorite, but... meh.
The thresholds are simply set so low, that most parties will fulfill them just by regular adventuring, with no need to take detours, performs quests or make sacrifices in any way.
This should be obvious for everybody to see. There is only a single "level" of better gear to find. Either you have a non-magical weapon or you have a magical weapon. (Sure silver and adamantine are sometimes mentioned, but without any real practical impact, since any old +1 weapon does just as well)
As mentioned, it hasn't been obvious in my experience. We had to go after specific weapons, and even obtaining some silver arrows required work.
Needing a +2 or +3 weapon? Gone!
Needing an anarchic or axiomatic weapon? Gone!
Needing a cold iron or adamantine weapon (with no substitutions)? Gone!
Magical energy based attacks are given to every first level spellcaster. And they're unlimited in all regards! Even fighters and rogues can have them (either by feat or subclass).
But those magical energy attacks both require expenditure of a resource that could be spent elsewhere and are considerably less powerful than the physical attacks of the fighters and rogues. Against a merely resistant foe, those physical attacks would probably still be more effective.
That magical energy attack comes at a cost and so should have a reward in those situations where it is relevant.
The book of supplementary rules coming out might have details about cold iron and adamantine weapons etc; how to obtain them and which monster resistances should be adjusted if those rules are being used. Its probably a good idea not to introduce a threat that requires a specific material or property to overcome before you introduce that material or property into the game.
If you don't like the "binary" nature of the default system, you could always just adjust the monster stats - perhaps making some higher CR creatures with immunities now also resistant against weapons of only +1. Just bear in mind that a +3 weapon is a legendary item of which even a high-level party may only have one. Or none.
I see it as part of a definite trend to make D&D... easier, for want of a better word. Very much easier. In order to make D&D run like it used to, you need to tweak everything yourself. Not one of these obstacles will ever be felt by a party running official modules, assuming baseline competency in creating a flexible party that covers the necessary bases.
Well, gee. Where would
you draw the baseline of competency then?
Look, I'm certainly not advocating for a return to the bad old days where a monster could resist 40 points of every attack unless your caddie pulls out the right club for the job. But it definitely seems like WotC thinks us gamers don't like setbacks and problems and being denied stuff, because this edition is ridiculously easy to beat.
(You know and I know I can throw a dozen Balor at a level 2 party. This isn't about that. This is about the default difficulty dial being turned down a notch or two compared to every other edition I know of, in every damn area. It's a significant and profound change that shouldn't be hidden behind conciliatory language)
I believe that 5e's ethos when it comes to immunities and resistances is to make things merely harder, not impossible. There is little "You must have X to succeed" gating. If a DM wants to make a creature immune to the party until the correct McGuffin has been found, or ritual has been performed, they can just do that by fiat.
