The sad fact of the matter is that flying is not what it was. Everyone wants to fly for next to no money, and yet the airlines' costs are forever increasing. The Brexit induced pummelling of the pound must be costing something like £150-£200m per quarter at the moment, and management are bound to be looking for ways to try and offset that. Who knows when the pound will rise again? IAG is not alone. Check out EasyJet's share price. Sadly EASA FTLs have been adopted as a target rather than a limit, but I'm not sure anyone expected anything else in such a competitive environment. Full-time shorthaul flying within the UK is no longer a sustainable lifestyle. There it is in black and white.
Most people are seeing longhaul as the way out, and so I guess they see BA as attractive even if they are close to a command at an LCC. Even if they have to accept a decrease in Ts & Cs in the short term by accepting a shorthaul placement, it is perceived as The price to pay to attain the goal that is longhaul flying. And then once you finally get to longhaul, all will be good. The flaw in that thought process is that I've flown with long haul DEPs who regret their decision to join too!
In my own personal opinion, longhaul in BA is still not bad, but the changes to lifestyle over just a few years have been severe. Unfortunately, I think it will only be a few more years before it too is unsustainable over an entire career on a full-time contract. It is the way of the world. Custom and practice dictates that BA say "Jump" and BALPA will say "How high?". Why does this happen? Probably because BALPA knows that to refuse will cost them and the pilots dearly.