But they'd then have no ignite or anything.
I mean, lets be honest, the summoner spells at the moment are set to a few things.
Flash is a must-have, unless you're Olaf or something and can take ghost. As an ADC, you basically NEED heal for your second for kiting and sustain and fast healing you and your support and anyone else around, as a mid laner you need that extra damage or defense so you either take ignite or barrier to block some burst, and as a top laner you need to take TP or else you're basically saying "fuck the front line I'm the carry," which is acceptable if you're someone like Darius, but otherwise not so much.
Rarely is anything else used. Cleanse is only ever used against a high-CC team that can actually be cleansed(stuns, roots, etc.), and near-useless against other teams.
And, itsn ot like it has to block the damage, just CC. So if a Blitz hook lands on you, you shield it, but the damage still goes through. It wouldn't do much against any mid laners except maybe Malzahar and his silence/ult which he can still do after since you can't anticipate it very well, so it wouldn't be too scary to see Zed or Fizz with it.