the detroit fellas were influenced by a broader range of european electronic dance music than most people realize. and there's a good argument that 1990s techno has as much to do with dark, minimalist 1980s chicago house as the relatively sunnier and jazzier 1980s detroit techno.
but the fact is that the detroit guys were the ones who made music called techno, and from which later techno directly descends. sure there are other antecedents, some perhaps as important for later developments in techno, but if you want to trace the history of "techno music," you have to look at what the term was first used to describe. that's the direct lineage, with other influences coming into play, and shaping the trajectory of that lineage at various points.