I understand how this can bug people, and this is not a refutation of how it would bother you, because I get that some people want monsters and PCs to follow the same rules. But it does reminds me of the first time I sent a Solo against my players in 4E, and my players asked pretty much the same thing. I told them the monster could do that because I **** said so. It's a fond memory, because it highlights one of the many ways 4E brought me closer to my old school gaming roots, especially on the DM side of things.
I'm actually surprised how many people oppose the boss tags as gamist, but that's often a criticism used by people who like older editions of the game where DMs held much greater power. I love the solo and minion tags because they unshackle the DM, allowing them to just design an adventure as they see fit and not worry about matching monster rules to PCs rules. I would expect more support from the people who like older versions for game design that does this for the dm.
I get that some people want monsters to follow the same rules as PCs and this helps the world seem more realistic to them. Me, I like that boss or minion tags let me gloss over the mechanics of a monster since I know they'll work and focus on designing the monster's place and purpose in the world. Fortunately this is one of those debates where both sides can have what they want. People who don't like the extra tags don't have to use them, and people that do can. It's perfectly modular design. Heck, even 4E allowed you to design an entire dungeon full of humanoids with classes or play an entire campaign without using a single solo.