The walker Chewie took captured took out another AT-ST, which surely had an impact on the battle. And was a speeder bike taken out by the captured AT-ST? I don’t recall.

And maybe the force did help in those other situations, since Luke survived those times, even though he hadn’t been trained much then. Also, it isn’t known how strongly the force was working in either side then - but Vader was present, so there was a strong dark force presence. Though Obi’s spirit could have been with the rebel fighters during their attack on the DS before he speaks to Luke.

During the battle on Endor, I think all force minds, living and spirit are focused on it at that point: Luke, Leia, Obi, Yoda, Vader, the Emperor (who seems to be overconfident and more into dicking around with Luke than concentrating on the battle).

Regarding a previous comment, the people, like general Ackbar saying “May the force be with you” are not saying it as a general “God bless you” type of thing, they’re saying it because they believe it, mean it, and hope for it.