On horizontal mobility in general, there's just a really large gap between who's fast and who's slow in run speed -- with and without factoring in Sonic who you could consider as an outlier because of the jump from first to second-fastest -- and walk speed. With run speed, it's kind of simple. The fastest is 3.5 with Sonic or 2.32 with Captain Falcon and the slowest is 1.15, Robin. There are characters who walk as fast or even faster than the slower runners. It's like the fastest walkers are jogging and the slowest runners are jogging... I remember posting about this where if you start at the lowest run speed, there are 27 characters who walk as fast or faster than Robin and by the time you get up to the fastest walkers, 2, Lucina and Marth, of them match the 1.5 crew of runners which isn't as insane, but still pretty bad that your run speed is not even faster than a few characters' walk speed. I feel like run speed and even walk speed have too low of a floor where run speed should probably have a floor of 1.4 or at least 1.3 rather than 1.15. At 1.4, only 6 characters would walk as fast or faster; at 1.3, only 9 would walk as fast or faster. Would it really make a difference? Maybe not, but it would be a quality of life change. Take Ganondorf. Would a run speed of 1.3 or his Melee run speed of 1.35 really break him? No. He's still slow, but not as slow. Now, Ganondorf with a run speed of 1.6 or something stupid like a run speed of 1.9. Okay, that's when King of Evil became Demigod of Evil. Crank it up to 3.5 and he'd definitely be a God of Evil.
Speeds around 1.6 to 1.5 aren't really that noticeable in difference. You could even extend it to 1.45. It's when you get lower and lower or faster and faster that things do make a difference, especially since the characters who have fast run speeds aren't as clustered together compared to the ones who have slower run speeds. There's 1 in the 3.5 range, 1 in the 2.3 range, 1 in 2.2 range, 2 in the 2.1 range, 4 in the 2.0 range, 3 in the 1.9 range, 4 in the 1.8 range, and 6 in the 1.7 range. For average, there's 8 in the 1.60 range. Going down, there's 12 in the 1.5 range, 7 in the 1.4 range, 4 in the 1.3 range, 2 in the 1.2 range, and 2 in the 1.1 range.
I guess the other thing is that compared to other games, sustained movement isn't as fast as in Smash. When you see characters move in games like The King of Fighters, Street Fighter, Tekken, etc., even with runs which is way more commital, they aren't like in Smash where you have Captain Falcon, Cloud, Sheik, or Yoshi blazing on through or even Mario running in. Most of them are done through walking which is also slower or dashing which... is kind of the same, but not really since nobody has a dash like SFV Nash's not even Fox or Little Mac.