I would actually argue there is insufficient time to cover the science curriculum in the time I'm given by the school I work at. Or rather, we have the time to cover the curriculum, but not enough time for practice. Pretty much every lesson I have to introduce a new topic, a new boat load of key words, a new concept, a new equation etc etc.
Obviously it does depend a bit on the class, but for e.g. an upper-middle set who are capable of grasping the content, but need a bit of time to go over it, ask questions, for me to check understanding and correct what's wrong, etc, there's not much time in class for them to get recall practice or to practice their exam technique.
Therefore, they get set homework, for my GCSE classes this might be past paper questions, it might be recall practice on Seneca, it might be to create a revision resource for a topic we've just finished etc- all things that unfortunately we don't have enough time to do in class. I do think the homework is worthwhile, or I wouldn't bother to set it.
If we did all these things in class, I think we would genuinely struggle to cover the whole course before exams start, and my Y11s are already asking me when we will "finish the course" and start revising (the answer to this is "soon" but they need to be revising in their own time too).
Unfortunately, I can't change the curriculum, or the way my students are assessed, so homework is really the only viable solution.
BTW, normally we don't have a TA in class unless we teach an individual child with a specific need, but even if I did, I'm not sure how that would help me cover content faster? Should myself and the TA deliver two separate lessons on two different topics? I'm not sure that would work well!