The sequence of events is the plot. What the plot is actually about is the story. And the quality of a story is determined or driven by its characters. Not in terms of what they're doing, that's the plot. It's what's
happening to them that drives the story.
AoE Optimus Prime is the only Transformer character who's had any development in these four films, so let's use him as an example (because there's no other

). In the beginning of the film, Optimus Prime has become a dark and embittered character. Having lost his faith in humanity, he has become spiritually lost. Through his relationship with Cade Yeager, Optimus Prime goes on a personal journey of rediscovery where he must learn to trust again. This is an arduous and difficult journey for him, as he encounters obstacles along the way as he delves deeper to discover the terrible truth behind the humans' betrayal against the Autobots. Now the problem is that this did NOT _drive_ the story of Age of Extinction. It was more something that almost happened in the background while other stuff was happening. AoE would have been a much better story if Optimus Prime's character arc were allowed to take centre stage.
Characterisation is much like the 'engine' of a story. The better it is, the stronger that 'engine' is the the greater drive a story has. Stories with weak character-development are like cars with weak engines. Yes, they can
function, they can move, but they're not great. A movie that has loads of spectacular visuals and thrilling action but weak characterisation is like a car with say the chassis of a Lamborghini Aventador, but the engine of a Holden Gemini.