The principle is the same. Your argument might've had legs to stand if the routes flown by the regionals weren't often the same as the mainline fleet.

No it's not, people who fly smaller planes which generate less revenue get paid less.

Yes, in general the more difficulty in filling a position, complexity, knowledge, responsibility, experience, revenue / profit generation results in more pay for employees.

I see what you did there.

Doesn't matter which of the big three you fly for, I need only say two words:
American Eagle
Delta Connection
United Express

You can't tell me it's not outsourcing. You can't tell me the pay and benefits are the same. There's a reason for the outsourcing...

you are paid (roughly) by how large the plane you fly is. 717 pays less than a 737 which pays less than an A330. Delta connection is not flying 737s, they are flying planes less than 1/2 the seat count. ( all 3 legacies cap RJs at 76 seats, 737 carries ~180) Just like Air France regional or air Nordstrom.

also a significant reason you mentioned is bankruptcy, prior to post 9/11 bankruptcies most majors heavily limited RJs in general but specifically those with more than 50 seats.

Regardless of your excuses and rationalizations, it's still simple hypocrisy. Don't scream at your neighbor for "harming the profession" with outsourcing and disparaging wages/benefits, while it's happening in your own backyard.

What about Lufthansa Cityline flying Lufthansa mainline A340? But nobody complains about Lufthansa

Star Alliance codeshares (and any other methods of increasing mainline profit sharing) are off limits to criticism on this website.

Looks like some folks actually get it.

Don't forget that there have been many times when mainline was shrinking and furloughing, while the poverty wage paying regionals were expanding and taking over routes formerly flown by mainline.