> The original sets a hypothetical stage and from that its conclusion, I think it flows better.

The stage is "years ago", and conclusion is "go.mod would not have existed and this would have an even bigger impact". My version re-arranges the sentence so that "go.mod not existing" bit is a part of the premise, not of the conclusion.

Tense agreement in English subjunctive is hard. Especially for non-natives such as me: I do parse the original statement like that and just can't bring myself to understand it otherwise.