The league is again transitioning to more hard-nosed, run balanced offenses and for a period, defenses that are still biased toward sitting back and taking away the big play will be forced to drop an extra man into the box to counter and thus will be vulnerable to strong rushing attacks and big plays off of play action.
Mahomes statement is simply recognizing this vulnerability and looking to exploit it. Over the past few years, the NFL passing game as a whole was one predicated on the short to medium game.
This is in part why guys like Russ began to struggle around 2020 when defenses began sitting back and forcing QBs to find the underneath routes and plays in the middle of the field. Rushing attacks had been devalued to the point they could afford to play safeties high.
A shift back to pre 2020 strategies on bith sides of the ball means that if you havr a string ground game in the next few years, the deep ball will be there again, as will the sideline routes that were better accoubted for by virtue of the fact defenses didnt have to hold LBs closer to the LOS.