MechaPilot
Explorer
If you can outrun and kite, then you can out run and kite.
Yes. That's true. That's one of the reasons why I always equip humanoid enemies with some kind of ranged weapon, even if the adventure or MM entry doesn't give them one.
In my experience, being +5 feet faster than your opponent is as good as being +50 feet faster.
So, the impact of +5 speed versus +25 speed, seems negligible to the gaming balance.
Additionally, the range of longbow keeps speeds irrelevant.
I can't say I agree.
Granted, if we're talking about a flat open area I think what you said above makes sense. However, taking a moment to look at the maps in the adventures I own reveals a fair number of relatively short corridors that do turn or have an opening into another room. With a +25 foot speed modifier, a character could easily get around a nearby corner or into a nearby room and out of sight of attackers.
The range of player speeds from 30 (human) to 40 (cat, wolf) to 50 (lion, elk) are all within normal beast speeds, and seem like something a legendary hero should be able to do.
To me, that seems like a better argument for +5 ft per +1 than your argument above.