Holding all primaries on the same day is a terrible idea
Then only the well funded candidates have a chance. The reason having a couple small states going first works well is because it allows relative unknowns like a Jimmy Carter to have a shot. They just have to make it past the initial filter.
One could argue that switching around which small states are first is better than it always being Iowa and New Hampshire, but both states being relative swing states helps too. Having a state like Utah or Kansas first would lead to much more conservative republican candidates, and who knows what it do with the democrats. Now maybe you think more conservative republican candidates are a good thing - both conservative republicans and democrats (because extremists on either side are less likely to win a general election) would probably like that outcome. But mainstream republicans and independents, not so much.
Given that a state both has to be small (to lower the cost bar for candidates) and relatively middle of the road politically, the number of choices is actually pretty small.