Do you wish you had kept 3e’s Ex/Su/Sp ability descriptors? Nope. My only regret in this regard is that we left the open-ended "magical effects" wording in some places.
Also, antimagic field is a funny spell in that it's the star of many internet discussions, despite not seeing frequent use at the game table.
— Jeremy Crawford (@JeremyECrawford) April 20, 2020
I wish he explained his reasoning.
I’ve always found it to be supremely useful to know at a glance how abilities interact with magic or spell nullification, since my players love that sort of thing.
You run into some big monster that starts to use some nasty ability. Is it spell-like? Then you can counterspell it! Is it supernatural? Then you can suppress it with an anti-magic cone or null-magic zone, etc. Is it extraordinary? Then the monster can just do it, no magic involved.
Now in 5E, if players ask me if a dragon can use its breath weapon in a null-magic zone, I have to create a houserule for which way I want it to work. And while that might be easy to figure out and remember for future sessions with dragons, what about weirder and less obvious abilities?
Without looking it up, do you remember if beholders fly naturally as a result of physics, or supernaturally as a result of magic? If a beholder is aiming its anti-magic cone at a PC wizard in one direction, can that wizard be freed from its effects and become able to cast spells if an ally drops an anti-magic field on top of the beholder? This is really important information sometimes!