Any time you miss a binding you are exposed to attacks with little to no contribution until the next binding. Compare Thresh, who can still trade with people with the autoattack passive and has a very useful flay and shield for damage, disabling and sustain. Morgana has no sustain at all (spell shield isn't meant to deflect harass) and the only use of her W is to quickly apply Frostfang's or to combo with a binding. Any time I see a first pick Morgana I pick Sona/Nami/Zyra/Karma and win the lane unless a lucky binding ruins the laning phase. Sometimes I pick Janna because against Morg it's like bypassing her subpar laning phase, and E-empowered autos go straight through spell shield while movement speed lets you juke easier. Morgana functions much, much like Blitz - a pick support with a rather binary laning phase - except she has way more utility.
Thresh's hitbox is also really stupid though.