Isn't that true even if we play 4-3-3 with 3 midfielders as CM should be in the position to progress the play and also support attacking players in more advanced positions? If we go strictly by positions on paper then 4-3-3 will have only 3 attackers. On pitch it will be very different, Bruno always make attacking runs from deep and if you see his heat map, he covers lot of pitch. Bruno won't be in 2 places at once but he will be all over the pitch dropping deep, beating offside traps, drifting wide.
Also I don't remember us playing rigid play style, at least under Ole. We play Rashford, Bruno, Greenwood as attacking 3 with either Martial or Cavani as CF. CFs always drift wide and players like Rashford, Greenwood make attacking runs into the box. Bruno pops up next to AWB to cross the ball, sometimes makes the run beating offside trap and then he is next to Rashford and Shaw playing short passes.
Also when it comes to defensive phase, Bruno will be the most advanced player, that's how we have set up all the time. He presses more than any player we have (maybe except Fred) and he always takes up very advanced position to press the GKs and defenders. If we are talking about our general defensive set up then we usually leave at least one wide player higher up the pitch as an outlet for counters along with CF.
Reading back, I'm not sure if what I posted is really a proper reply to your posted but just wanted to post it anyways
Leaving all this, when was the last time we saw 4-2-3-1 shape on the pitch when we attacked? All I'm trying to say is, when we attack, our players have the freedom to move all over the place, so the space left by Ronaldo won't be occupied by only Bruno. Rashford, Greenwood also does that. Forget attackers, even our CMs make attacking runs into the box all the time.