IMO, I think that future sentai series should do something like Goggle V or Bioman did when it comes to mecha battles. Those are two sentai series that have done something different in those that the other 34 sentai series didn't, in which they usually have the MOTW's grow big or that the monsters grow big by themselves (From Battle Fever J to Sun Vulcan, Dynaman, & from Changeman to present).
In Goggle V, whenever a monster is defeated, the giant mechas that look exactly like the MOTW's gets sent down, revive the defeated monster, & have them piloting on their mechas!
In Bioman, there were no MOTW's, it was either Psygorn, Mettzler, Zyuoh, Messerju, or Aquaiger that acted as the MOTW's of the week. After they were defeated, Doctor Man usually sends down the Mecha Giants (though starting on episode 31, the series started having either Farrah, Mason, or Monster piloting on them).
In Goggle V, whenever a monster is defeated, the giant mechas that look exactly like the MOTW's gets sent down, revive the defeated monster, & have them piloting on their mechas!
In Bioman, there were no MOTW's, it was either Psygorn, Mettzler, Zyuoh, Messerju, or Aquaiger that acted as the MOTW's of the week. After they were defeated, Doctor Man usually sends down the Mecha Giants (though starting on episode 31, the series started having either Farrah, Mason, or Monster piloting on them).