Don't confuse fairness with market forces.
Most people would regard it as fair to be paid from day one of company induction or groundschool. You are, after all, an employee. That's how life works in most industries.
Unfortunately, in this industry, some people are so desperate to fly that they'll sell their granny for a first job. Pay for an application? No problem. Pay for a type rating? Sure. Pay for 'line training experience'? Why not? Never mind that in the long term it erodes everyone else's terms and conditions by encouraging management to force ever more training costs onto the individual. Who cares when all that matters is getting into the RHS of an Airbus or 737 with 200 hours.
Such is the aviation market, and that's what dictates when and how much you get paid. Fairness doesn't come into it.