Lyxen
Great Old One
Many actions of creatures have the wording "+4 ranged spell attack" or similar (see Flameskulls). This does not mean that these actions are spells. It does mean they are magical.
Can you please elaborate why this does not make then spells at some level, in a 5e where natural language is used ? Or considering the SAC, which mentions, amongst the criteria "Or does it let you create the effects of a spell that’s mentioned in its description?"
(AFAIK, "spell" attack means it uses the spellcasting ability score to determine attack bonus, and that's about it. The magical part comes from Sage Advice's ruling on whether a dragon breath is magical).
On this one, I completely agree, they are magical and therefore counting for the most important thing which is magic resistance (which can affect quite a number of PCs).
The new War Priest has a Holy Fire ability that has no attack in it; it's a saving throw. By the same ruling, that action is NOT magical.
It's a bit hard to read honestly, a single word can make the difference for those who actually want to apply things extremely RAW.
But the intent of these changes is that Holy Fire is a spell, from what I can gather.
I'm not sure what the intent is, honestly.
Compare with the Death Knight, who throws a "magical ball of fire". That's not a spell, but it is magical, because the text says it is.
"Hellfire Orb (1/Day). The death knight hurls a magical ball of fire that explodes at a point it can see within 120 feet of it."
And this is why the changes in TWBtWL are very minor, there were already a significant number of traits working that way even in the original monster manual, the death knight was actually using fireball in previous editions (I have not checked all of them, but it was the case in the Fiend Folio where it first appeared, "generate a 20-dice fireball"). But because it's a magical damaging attack which is major in its arsenal, it was already separate despite the fact that it would have been really easy to put it in the actual spellcasting trait of the knight.
I do note that we're delving into things that are badly defined by the rules. Indeed, a large part of them do not exist in a good state in the rule books. It is eye-opening reading the Sage's explanation of "Is the breath weapon of a dragon magical?" and realising that this answer is made up of whole cloth.
This is the part where I wholeheartedly agree with you, this was slapped on as a complete afterthought, and it's really lacking. It's one of the 3e things that I think could have been kept without them making the game too technical, the tags for the magic type. While I understand that they immediately make the game much more geeky and including much more technical jargon, it's one of those areas where it's fairly fundamental to the game.
That being said, it has NEVER caused any problem at our tables, we have been playing 5e twice a week at all levels since it came out, and the local rulings of the DMs have always been accepted by the players without any discussion, because they felt logical and in the right mood every time.
And, because of this lack of definition in these rules, we're running into a bunch of player abilities (and monster abilities) suddenly reducing in value.
Honestly no, some gain in value, some reduce in value, overall, once more, the effect is really minor across the game.