Multistrike repeats can be cancelled, but not Spell Echo repeats.

I believe this is an intended feature of the game. However, the wording of both support gems is the same "Supported Skills Repeat # additional times", so I believe they should receive the same treatment, such that you can cancel Spell Echo's repeated spells before they occur.

you have one less repeat on spells, you should be at range most of the time.

This isn't a bug, it is something you don't like, as such this is feedback and should be moved there