It is not possible to control tamed horses anymore even with a saddle. It seemed to work in 40b. It also appears impossible to tame a horse, it will run around but never throw you off and will never be tamed.
Reproduce controlling:
Load map from 40b.
Find tamed horse with saddle.
Can't control it, it won't move.
(optional) remove saddle, add it back. Still won't move.
Reproduce taming:
Spawn horse with mob-egg.
Jump on it.
It will not be tamed and you won't get thrown off. It will still run around like when you jump on an untamed horse in previous editions.