Still disagree. The DM controls the reward of XP. That is the power of the PCs.
And there's nothing stopping the DM from boosting the monsters, throwing infinite dragons at the PCs, and playing the monsters as smart, thinking creatures who generally don't want to die...as long as that all applies to a given monster. Nothing stopping DMs from having flanking monsters or monsters fishing for advantage.
Agency is a weird one. To me, agency isn't the players being able to choose anything that's printed in an official D&D book. Agency is the player having the ability to effect the world their character exists in. If you use the illusion of choice, that destroys player agency. Railroading destroys player agency. Limiting character creation options does not.
5E seems to have two big things going for it. 1. It's where the players are. 2. Dis/advantage. Beyond those two, it's not drastically different from any other edition of D&D. Most of the same basic rules, same general ideas, though the particulars here and there are different. You could remove a few things, tweak a few things, and roughly replicate any older edition with a bit of work. Though admittedly, some of those differences are huge. Superhero healing, PC power scale, etc.