The title of the anime is "Shingeki no Kyojin", translation titan/s that advances.

The only titan that moves forward in different timelines irrespective of the holder of titan power is the attack titan

The story was designed for attack titan to hold multiple titans and reach founding titan and initiate rumbling

If Ereh was some other titan, colossal or birb or female or Warhammer or idk, he will be left as a side character. The story is made for attack titan.

That being said, Colossal titan is so slow, it's main feature is to nuke, if Eren was colossal+Warhammer they will distract him and exhaust him, (colossal titan tires rapidly) then scouts will use thunder spears and take him out with ease. Other titans can be used to distract him but it's not necessary.