Looking at it objectively, it would seem to me that seniority must push down T&Cs for pilots. If people felt able to pick up and transfer to another, better paying, airline then surely there would be more pressure on airlines to offer competitive pay. As it is, most of us are trapped in our current roles and subjected to the all encompassing zero costs mindset that pervades this industry. Many copilots in my outfit are more than qualified for Command but stay where they are because the seniority system has trapped them.
Perhaps those who fell for the low-cost expansion, quick command, Emirates transfer is now paying the price for their decisions. I left low-cost command, joined a career airline (with seniority!) at the bottom, took a huge pay cut. But it got me where I wanted to be in life. I'd be utterly miffed of some top gun of my age, with a few thousand hours 777 command, would join as DEC. I served my time, stood down the money and now it's pay back time.
Not sure what you base your allegation that seniority drive down T&C. On the contrary, seniority airlines often have group of pilots who don't move. They don't vote with their feet, they take the fight. And they're not all going bankrupt, if that's your next argument.
For those loosing their jobs due to bankruptcy (such as Thomas Cook), I sympathize. But it doesn't warrant to give up the whole seniority bit. Life is full of gambles, some which are beyond your control.