I can see this from two sides as I was an LSA before becoming a teacher. My husband is also an LSA. Yes, LSAs are underpaid. My husband works in an alternative provision centre for excluded children and is on £14,000 take home. This is a place where drugs and knives are brought in, fights break out and staff have frequent verbal abuse. Nature of the job but so underpaid for the type of work and environment.
For me, I was happy with my LSA pay initially as it was my first proper job out of uni and it was the most I'd ever earnt. However, I soon realised it wasn't great.
What I would say though, a starting salary for a teacher (in my opinion) is worse. For many teachers they will have paid out a lot of money to train. Then there's the ultimate class responsibility, the hours, the pressure, the workload, the grilling on progress, the accountability. LSAs don't have those things although I know their performance is more scrutinised now than ever before.
In my first and second years of teaching, I had a nursery nurse as my LSA because it was reception. She was earning a lot more than me both those years because of the grade she was on even though I was doing more work. She was excellent at her job so deserved her money but my point is, NQT wage is shit basically!
One big bonus to being an LSA is leaving school work at school, despite the crap salary. With teaching, your evenings and weekends are not your own. There's always work to catch up on. I'm on mat leave at the moment but I'm seriously considering going back into an LSA role. Big salary drop, especially from m6, but you get more of a life.