Why does RIOT keep making healers if they clearly dont want heals to be any good?

Yummi is just another example of this, her heal is laughable, even when it get the max bonus from missing health, honestly, a 130 Heal at a basically 14 second Cooldown, and to get that 130, you have to wait until your target is at 20% HP...

Even if you use both Stacks, you will end up with like 200 healing, on a 28 second cooldown, (and this isnt like Taric, where the low heal is balanced out by being AoE, double aoe and spammable as long as you stay in combat)in a game where even tanks do at least 200 dmg with each hit and 300+ with their 3s or lower CD spam attack...

I get it, healing isnt fun to watch, it doesnt kill people, but why waste a champions spell slot with a heal when you want to make it trash anyway? They could have given Yummi something usefull instead...