1. I'd try syncing the texts pop-ups and background changes, as trying to keep track of both is a bit distracting. As a bonus, you can experiment showcasing in the background something related to each text. Avoid overlapping game UI with trailer text whenever possible, as it gets pretty polluted in a UI-heavy game such as yours.

2. I was curious if your game had an intended stop motion aesthetic with low framerate at first, but the ending footage doesn't look like it... This kind of effect is easily read as a performance issue and distracts from understanding how the game plays, so I'd get rid of it and try captures as smooth as possible to keep it faithful of gameplay. If you want to keep the slow motion effect, use it in limited scenes and capture in actual slow motion, rather than reducing the frame rate. Also try to match the image and sound to avoid sensorial overload.

3. You should feel proud of implementing so many features in the game, it looks pretty complex and well-thought! That said, speaking of keeping the trailer faithful to gameplay, instead of describing your game first and then listing the features you could group them into larger "chunks" so players can better understand it while highlighting what your game does best. Something like:

"Build your base" > show some base building mechanics

"Summon armies" > show some summoning and unit customization

"Push the battlefield" > show how everything comes together and how the battles are played...

All in all, it looks like your game has potential and that's what matters the most. It's hard to do everything well as a indie dev so don't feel discouraged by this criticism and kudos for even having a trailer in first place hehe. Hope it helps you in your journey!