I want to preface this by saying I don't disagree with the idea of the universe's expansion, this was just a random thought that popped into my head. I also apologise in advance if it's a duplicate, badly formatted, fairly simple or outright dumb (I'm very sleep deprived and haven't looked at the intricacies of the universe's expansion in a long time + I'm on mobile).
on to the question; how do we know that the redshift we observe while looking at faraway galaxies isn't a Doppler shift, caused by potential great attractors outside of the bounds of our observable universe? are there galaxies that have travelled "faster" away from us than galaxies that are in the same region of space, but further away from us? if not, could this also potentially explain the differences in the perceived rate of expansion depending on what region of space you measure?