Yes , Yes, Yes. I so agree with the poster. Having a TA working with children in the class means that many children rely on her to tell them what to do, rather than listening and being independent. The TA's intervention conceals the child's true ability; the children become increasingly dependent, and a vicious circle ensues.
As for managing a class of 30 4-5 year olds on your own: what do you think we used to do in the 60s, 70s, 80s, 90s? I started with 38 children in Reception, just me, and they came to school wearing ties, belts, shoelaces, button -neck shirts; we managed, and I had to hear them read every day.
Discipline was stronger, and the children didn't receive mixed messages.
TAs are necessary now because of the ridiculous impositions assessment makes on a teacher's time. Looking at the dismal primary education results, 26th in world ranking, children are not doing better now, despite all the help they receive.
I could go on, and frequently do, sorry. (some of my best friends are TAs!)