It's time this job was re-framed and re-categorized. Since the TA was originally introduced the role has metamorphosed from something that quite likely started off as something more akin to the 'glorified pencil sharpener' to something that is much more specialized, but insufficiently defined.
The first thing that needs to happen is that no TA, whether HL or not, should be doing the job of a teacher, and they certainly shouldn't be teaching whole classes independently. People in that profession have QTS for a reason; otherwise what is the point of the degree/PGCE? TAs' roles should be complementary, not supplementary. Some are brilliant in dealing with children who are on the spectrum, and are appropriately qualified to do it. Some are great at running individual phonics groups with specific sets of children in the early years. They perform a huge variety of tasks: some menial, some highly specialist.
NB. SEN support is commendable and necessary, but as support. On the continent there are certain countries with more clearly-differentiated set of roles in schools. For example, unlike in the UK, teaching and classroom management/crowd control are distinct jobs, each performed by the people who are qualified to deal with those specific issues.
A TA's role shouldn't be 'all things to all people' or 'glorified pencil sharpener', or 'teaching on the cheap', and people have different ambitions and very different reasons for doing the job. Some want 'menial'. Others are dedicated to the often invaluable support they offer, sometimes to children in desperate need of it. If the TA label has outlived its usefulness it could probably help to redefine this roles, to ensure it's kept entirely separate from the teachers' roles, and to pay people a proper salary for fulfilling it.
Somehow, and for obvious reasons, I get the sense this won't be happening any time soon.