Malz ult is not ok.
Malzahar channels the essence of the Void to suppress an enemy champion over a zone of damaging negative energy.
Malzahar suppresses a target champion for 2.5 seconds, dealing 125/200/275 (+80% Ability Power) magic damage over the duration. A zone of negative energy is created around his target for 5 seconds, dealing 2/3/4% (+[1% Ability Power]%) of nearby enemies max health as magic damage per second.
Yes, it can be removed with QSS, but that requires everyone on the team to spend 1300g. 1300x5=6500g. So either you lose a member of the team every 48 seconds late game, or you put your team at a 6500 gold deficit.
It needs to either be a skillshot, have a longer cooldown at max rank, or not deal %HP damage. Something. This ability is an idiot-proof point-and-click delete button.
self cc ultimate, only deals damage, can be escaped with mobility.
self cc ultimate, only deals damage, cannot be escaped with mobility, but is telegraphed and can be shielded / prevented in other ways.
self cc ultimate, slows and deals damage, has a very long wind up, can be escaped with mobility.
self cc ultimate, deals no damage, knocks back enemies and heals allies.
self cc ultimate, suppresses target (not reduced by tenacity), deals %HP damage in an area around the target, cannot be escaped without spending 1300g on an item after which point he can simply target someone else with it.