The BA pilot pay structure chooses to reward loyalty. When you start, you earn below market rate (particularly if you obtain an early command), but you do so in the knowledge that your salary will rise over time and then you will one day be earning a decent salary. This actually benefits BA, so much so that when considering moving to a flatter pay structure several years ago, it was decided it would be far too costly to do! In my opinion, fair is being paid in accordance with what you signed up for when you joined the company, together with any negotiated changes thereafter. If you did not like the terms and conditions, why sign the contract? Given the above, it is common practice (certainly within BA) for new entrants to gradually have lesser terms and conditions because they can be more easily adjusted to reflect the ever reducing new entrant market rate.
As an example of how this benefits BA, I have only relatively recently started earning that higher wage and as it arrived I went part time. So BA have done rather nicely out of me - a full MPE at below general market rate and then a fraction of an MPE when I started earning that more costly salary. My lifetime earnings are considerably below those of an EasyJet pilot where such a salary structure does not exist.
For the cabin crew, yes I totally agree that many of the legacy crew are on a very decent wage. Do they deserve it? Yes I very much believe they do. That is the salary they were recruited on, and which was negotiated throughout their careers. Would BA like to reduce their unit costs by ending those salaries? Of course they would! But you cannot just change someone’s salary without negotiation - that is not playing fair. It has always been likely they would have more negotiating power to achieve their aim, once MF numbers were high enough. Just at they closed NAPS once BARP numbers became high enough. It is the game that BA plays. However, fire and rehire is totally unacceptable. That being said, whilst BA are going about this in a very aggressive way, I think attempting to avoid being consulted with at all, is a dangerous game to play.