Heroes like UB and Sedna are basically overpowered due to the amount of +% speed modifiers they can get.
Their speed is fine, learn to live with it. If they are stacking speed, you can stack hp and damage. They might reach you but cannot kill you and eventually they need to run away to regenerate. Then you can slowly advance on your lane. Rinse and repeat.
Also nerf UB's stun so it stuns for less time.
Actually the UB stun is both ways, UB cannot move either while you are stunned. Use it to your advantage, have your teammates wail on the UB while he is self-stunned.