I can't imagine Boyega is happy at this point. He's been the most obviously enthusiastic Star Wars fan of the sequel cast. If any of the cast ends up blasting them in public at some point, it will be him (or a hammered Oscar Isaac).
Amongst the main cast, he's the equivalent of Phasma for the supporting cast.
They waste him in TLJ entirely and they never really do anything significant with him in TFA (though in contrast to Phasma, he had his moments in TFA).
Kind of ironic considering that his character was probably the only original thing in this shitty new trilogy, what with being an "ex-trooper" which was sadly not even used to its full potential and was poorly executed, and not by Boyega, but by Abrams just having a guy who was brainwashed for most of his life suddenly rebel after seeing action for the first time and just handwaving that away by claiming he was a janitor, but even that begs the question as to why they would send a janitor out on a massacre despite having no real training, and its all made even more ridiculous when MSE droids are basically the janitors on board these things. Yet despite all that he's still somehow the only decent character and the only thing I liked from TFA. They could've had him be a regular rookie soldier kidnapped by Poe to try and escape the ship and then having FN explore the real world for the first time, and throughout the whole thing wanting to secretly go back to the FO while at the same trying to adjust to the realization that the order he once served was not as noble as he had been led to believe.
I wouldn't say the ex-trooper thing was not used to it's fullest, I would say it wasn't used at all, full stop.
There's 2 instances of him going "Oh, [McGuffin]? Sure, I used to mop the floor where it is stored", strangely enough after voicing his surprise that [McGuffin] actually exists. I hope they'll do it again in IX, btw.
Other than that, you really don't get any vibes or hints of Finn being an Ex-Trooper.
One of the many possibilities to go with in TFA which would not have been ripping off ANH would have been ripping off "Enemy Mine". I mean, have Poe and Finn spend some time on Not-Tatooine at the start of TFA, where they are forced to rely on one another, even though they really hate each other's guts. They could exchange some neat dialogue and ultimately, we could learn something about the Propaganda the FO uses to indoctrinate people. They start off as enemies, become friends after Finn realizes how much he has been lied to.
Then again, Finn stranding on Not-Tatooine and meeting Rey and them escaping in the Millenium Falcon in a wild action scene was one of the better parts of TFA (dat BB-8 thumbs up), I would just change a few things. Namely replacing the Millenium Falcon with a ship used by Rey, some old junker that she uses to haul scrap, cause having the Millenium Falcon randomly stand there is just painfully stupid. Them fixing it is painfully stupid. Rey randomly being able to use it so well is painfully stupid. Them meeting Han instantly is painfully stupid.
Making them escape in a scrap-hauler used by Rey would also explain why she can fly it so well. A turret wouldn't make sense on such a ship, so Finn could man some sort of crane or harpoon like device to fight off the TIE Fighters, which in turn would open up possibilities to be more creative than generic pew-pew.
The scrap hauler itself could be owned by that blobfish looking guy and the scene where Rey and Finn "fix" the Millenium Falcon could be replaced with them hotwiring it to take it.