I'm not persuaded by the "5e doesn't really have any rules anyway, only guidelines" argument.
Then too bad, it's clearly what the devs intended.
And there's a wide gulf between "people who don't trust their DMs" and "players who would like to understand how their abilities work without having to ask their DM to clarify them, and would like those abilities to make thematic sense"
And in these case, it's not your abilities as a player, it's only NPCs and monsters...
—as there is between "RAW addicts" and "DMs who would prefer not to add house rules where none were necessary before."
And again, although once more it can be played in many equally entertaining ways, 5e is not even about house rules but about rulings that don't necessarily want to make their way into house rule. You can (and probably should) make a local ruling for each individual NPC as to whether a given trait is a spell (or a magic item, or an innate power, or whatever else), you don't need to make it a "house rule" that would apply to all future NPCs. As the devs say this "would be counter to the open-endedness of D&D", why tie all your future games on the local decision made for an NPC, moreover one that you probably don't even need to make, since when using the power, no-one might even have counterspell ready, or a chance to perceive the casting and do anything about it ? Just make a simple ruling if the situation arises, no need to over think it and over design it in advance...
A little polite disagreement amongst fans about the value of new rules changes is hardly out of line, and in my opinion the response, both positive and negative, on balance has not been disproportionate to the changes.
And for me, it is inflated waaaayyyy out of line with people (not you) whining all over the place about their precious counterspells, mage slayer feats, and "right to know when a spell is being cast". Not to mention all the expert designers (despite not having ever designed anything of note) around here (not you again) who claim once more that the people who have designed the most successful TTRPG game ever, and who have finally brought that hobby into a respectable spotlight are basically idiots who have no idea what they are doing and who have, once more, done something idiotic.
Incidentally, I like the statblock changes for the most part, and I agree they're likely to improve the performance of DMs, especially DMs without extensive experience. I don't mind losing upcasting, etc. I just think that "magical actions" that are clearly mechanical expressions of regular ol' NPC magic-user spellcasting should count as spells, and I also think that RAW they clearly don't, and I also also think that RAW do matter, even if of course it can be ignored or discarded.
Of course it can, it can be ignored, discarded, improved, made to suit your table and your game. These are just new possibilities and even if you are using the published module, you are free when you run it to use the abilities any way you like and to allow counterspell and mage slayer if you think your players will enjoy it more.