SPT AKI deleting game files, causing crash

that is normal behavior, it launcher deletes files SPT does not need when you first run the game.

additionally, your game client version is compatible with SPT-AKI 1.5.1 please check FAQ to see how to make it compatible.

It looks like you have made a mistake while installing somewhere along the line. It is very important to check that the game version matches what is required. Both for AKI and for the patcher (will patch from one specific game version to a second specific game version , you can potentially use multiple patchers in succession even.)
Full instructions can be found in the documentation and in the FAQ.

Genuinely I mean no offense, but if you had done it correctly it would be working.

you could try giving more details than just "error after error" what exactly does the error say?

were there any errors when you ran the downgrade patcher?