I'm sure you've heard this a million times, but these UAs just aren't balanced for MCing yet. I'd be willing to bet they don't even consider it when designing so as to not restrict themselves. That being said, the only Prof they get is light armor...so light armor, I guess. The Strength of Mind thing will obviously need to be addressed....maybe if you aren't proficient in WIS save you just don't get it. It's a cool feature, so I'm glad it's in there in the first place, even if they don't have the kinks worked out.
Of course, I am just discussing this from a community-balanced point of view. Finding out what needs work is the purpose of the testing after all, so multiclassing is almost a requirement before a survey.