I can't come up with a good reason for this, other than I can't come up with a good reason against it either.
It wouldn't be terrible to simplify the system a bit. Right now, we have three speed related variables: speed, stamina capacity, and stamina recharge. It might be better to just consolidate them all into stamina recharge. The others are hard to communicate to the player. But on the off hand that this guy wants the current speed upgrade and stamina upgrade to be combined into some super skill, that's just fucking OP.
That's like saying combining Health Upgrade and Health regen. Sure, it seems to make sense, but come around to lategame and everyone has steroid survival, crazy fast speed and stamina, with two other skills on top!