flash should be replaced by mark/dash
i feel like with a more reasonable cooldown and range than on the howling abyss, changing flash into this spell would finally balance it in comparison to other summoners.
it would still keep its potential for flashy plays, but be less reliable and not necessarily the 100% to go summoner anymore. making ghost an equally attractive option as mobility spell to chase or escape.
even though you could probably still use it to escape lee sin style over a wall by using it on a jungle camp, it would probably have mroe of a purpose for agressive plays most of the time. while ghost still would exist as an option for escapes.