I'm 30 at a moderate elo and climbing, I'm currently on a 16 win streak with malzahar so he cant be that useless...
Yes cleanse does suck, Yes plenty of people use it but it DOES NOT make malz useless
People just play malz wrong, hes all about zone control and support damage. Malz doesn't start fights, he ends them with well placed spells.
TIPS FOR MALZ:
Since malefic visions does small damage over time quickly magic pen runes boost his damage significantly, with that said sorc boots are a must on malz, mercs are nice but if you're in CC range you're in the wrong position in the first place
before you have a ton of ap ( lvl 6-11ish) use his ult to stun, cancel and then use your full combo. hitting with null zone + call of the void + malefic visions + ignite is always going to be more damage early on and you can avoid being food for melee dps
if the enemy has 2 or more high health champs, ALWAYS get deathfires grasp. you can easily hit 45-50% current health late game every 60 seconds, I have killed full health 6k hp chos 1v1 in 3 seconds with DFG and a full combo
Malz is mana hungry, get a tear asap so late game you can take advantage of his ridiculous AP ratios and spam to your hearts content, Mp5/18 seals are a great pick for keeping malz in lane and become better than flat @ level 5!
Rylais is an absolute must, it makes nullzone a great tool for controlling the positioning in a fight and for covering retreats, and its slow duration refreshes until after the last tick off MV
Call of the void allows you to scout into fog of war, use it for bush checks and around corners in the jungle, you can even check the river sidelane gank bushes from around the corner within the safety of your towers range.
Pay attention to your minion, when summoned it will go after the closest hostile target. This includes enemy champs next to a tower, this will draw tower aggro to you not the minion!
If you are not mid try to lane with a champ that has a spammable or long lasting AOE to get the most mana return you can from MV, great lane mates are Morde, Nasus, and Cho
Null zone delivers its first tick of damage instantly, use this to finish off runners.
A good Malz build:
Sapphire + hp pot
rylais (belt first)
after this build to what the opposing team has
need to spam alot of spells asap? finish archmage
low death and plenty of assists? mejais
enemy stacking magic res? voidstaff
high hp team? Deathfire
get archmage now if you havent already
lich (if the match has gone this far then this is your best pick, extra burst and the move speed can and will save your life)