I would actually say go 152+ because that outspeeds +1 kyurem, which can stop a dd or scarf set (which is hella underrated rn) from getting out of control, or if you don't care about kyurem, 104+ because that outspeeds scarf lando-t and +1 gouging.I'm convinced many people just don't use D-Speed correctly. I'm also guessing many sets are also built a bit inefficiently because the typical recommended full speed invested is wrong. You simply can't count on D-Speed as your form of speed control because of the boosted metagame. But mons like Pult and Zama are in somewhat similar situations with their speed tier. D-Speed is faster than both with no speed EVs and only a + speed nature, freeing up all your EVs for elsewhere.
On the other hand, max speed + nature D-speed doesn't even outspeed Jolly or Timid booster speed Iron Treads or Scarf Enamorus. You aren't going to outrun most relevant BE or Scarf mons even with full investment. So why bother? IMO, there's really no need to worry about the boosted metagame with it. When I run an attacking set, I go 252 EVs in Atk and SpAtk with only a + speed nature. No speed EVs. Hazard leads likely also run a + speed nature and get away with minimal speed EVs compared to maxing it out like most recommended sets do. It is simply a waste. You could run more bulk and/or power EVs. It would be a lot more efficient to let its teammates worry about the boosted metagame like most players do with Pult.
Problem solved? How? Tusk loses to Tera Flying Acrobatics. So can Zama. Kingambit loses to EQ coverage and no Tera or Tera Fairy since Sucker Punch is resisted. Now that I think of it, Tusk also loses to Tera Fairy. Zama is hit super effectively by Fairy Tera Blast, and depending on Moon's boosts and if it is Zama's first time in or not, it can be vulnerable to it. Problem not solved. It's highly situational at best.
And if you think you can solve it with a Tera for Tusk, Zama, or Gambit, you had better deal enough damage in return that first Tera turn. Otherwise, you'll be vulnerable to getting KO'd by different Moon coverage and not stop it.
While you are correct that it outspeeds everything, Deo-S should be used to outspeed some slower +1 mons, which can be a lot more devestating. With the first ev spread, you can go 176/180 evs and the second ev spread you can go 200/204, which is still plenty powerful.