It has literally never been shown anywhere that making it easier to fire people makes for better employees. It's just a doctrine of faith news channels regurgitate because they're owned by billionaires who hate workers and labour power.
You can so easily spin it the other way, that making the lives of teachers easier to fire will make their lives more precarious and insecure which will stress them out, make them feel devalued and disillusioned, and make them perform worse.
Like what specifically can a teacher do because of unions that should get them fired? All the things they obviously shouldn't do are still grounds for dismissal with the full support of the union.
Plus if you took away all the labour rights of teachers to create a """competitive market" and it actually worked, which there's absolutely no evidence it would, wouldn't that just reinforce the pattern of rich schools having good teachers and poor, community based schools having shit ones, so you're actually just hurting poor people?
What you'd have done is made teaching a less appealing profession by removing all the union benefits that are its best feature now, so you're not going to get a flood of new teachers. It will just be moving around the ones already there, and the best case scenario is the good ones just get funnelled away from the kids who need them most..