Why is it programmed to predetermine winners in Overdrive matches?

It doesn't, we have stated this before. We try to give a roughly 50% win chance via matchmaking, but that's it. 

That said, you've certainly described some odd behaviour. 

If you have recording software I'd be very interested in seeing a score drop at the end of a match, that's something we need to look into.

Any clip of strange lineman behaviour would be appreciated too, that's super-useful when we see the AI/physics do something improbable.