Well my post was mostly intended as a joke, but does represent my actual opinion. So, okay, I'll answer.
I'll admit it's more complicated than the current system, but so is having a table of weapons instead of having everything just do 1d6. Yet many people clamor for more weapons. So then we get to the "needlessly" part, which moves us to your next two assertions...
It looks like we agree that it is more complicated. My "needlessly" qualifier is due to the opinions below, as you noted.
You may not think some "features" of the current system are actual problems, but others do. There are many examples just in this thread of the effect that a fixed rotation of turns introduces. There's also the perennial "realism" problem, and while I acknowledge that everybody has different thresholds/filters for that, it doesn't make it any less real of a problem for those whose thresholds have been crossed.
Yeah, I don't see any rule problems caused by the current initiative system. There are play styles that are encouraged by the fixed order, like planing your action based on who goes before you and who is next for example, but that is not really a problem. Unless you just don't like it, maybe?
"Realism" could be a problem, but honestly I think the default initiative system is just as "realistic" as Mearls' new system. In that neither is very "realistic". If you wanted more realism you should break everything into segments and everyone can move in 5' increments one at a time. Then attacks and spells would start from the point you stopped moving. Or something like that. But just making the order random every round and penalizing characters with bonus actions doesn't add "realism".
But if you just like the randomness? Sure, personal preference.
Now this one has me flummoxed. How does it reduce player agency? I suspect we are defining the term differently. Do you mean because there are fewer possible permutations of how to use your action and movement? That's fewer player options, not reduced agency, in my book. And I'm ok with it because some of those current options are so inexplicable narratively that I'd like to see them go.
In the sense that something might happen during a round that you might want to react to, but since you rolled poorly there is nothing you can do about it. And if you roll poorly on the following round there is a good chance you won't be able to do anything at all. In the Mearls system you are locked into an action that you decided on before you even know what is going on.
With the initiative as written, on your turn you can do whatever you want. It's your turn. Have fun!
But hey, maybe you like that. Seriously, I get it. People like different things and I can understand the appeal. But on the other hand I know a lot of players that will just get frustrated and quit if you try to tell them they can't do anything on their turn because they made the wrong call at the beginning of the round.