That applies to the private sector, where failing to maintain staffing levels means going bust. In the public sector however, the government has no such incentive and that has lead to combined classes of 60 kids being corralled by an unqualified "cover supervisor" in the school hall because schools can't recruit/retain teachers. Similar issues in healthcare, and we've seen plenty of chaos on rail as a result of driver shortages because the government isn't exposed to the same market forces that the private sector is.
None of this negates what I said, nor does it demonstrate that staff would be on minimum pay without unions. Indeed school and healthcare staff typically are in unions or, if not, there are sufficient numbers that are, for the unions to become involved in pay talks.
I'm not sure if you're trying to compare pay, but I think most people would agree that - generally speaking - if you compare rail sector jobs to education sector jobs, the former are generally more likely to be 'better paid' than the latter, so any issues relating to retention and recruitment are more likely to be greater than in the rail sector.
If your argument is that there is a skills shortage, or that skilled people are choosing not to do jobs because the pay isn't good enough, then you may be right but it really warrants a thread of it's own, with caution taken to make comparisons between sectors as there are various factors at play that means you can't just make conclusions based on anecdotes.
Bringing it back onto the subject of Network Rail, it's important to remember the circumstances that lead to the Clapham accident. BR's failure to keep up with the market rate meant skilled staff were in short supply.
If you're trying to suggest that anything unsafe is happening, I would suggest you elaborate and raise the alarm with the appropriate bodies.