Just some broad thoughts about scope and the major US pax carriers that are affected by this issue.

Since the Delta pilots are sharing their pain with their current TA, a lot of interesting stuff is being talked about which, ultimately, will affect all US pilots, mostly the youngest, whether currently on a seniority list of wishing/dreaming for a career flying big airplanes for big airlines.
I am not a Delta pilot and don't have a direct dog in (their) current flight, I do have a strong interest in the collective improvement in all terms and conditions of American professional pilots, including whether they will even have the right to fly (their) airlines passengers both internationally and on their smaller gauge aircraft.

The Delta details of their prospective working agreement sheds light on both the top end and bottom of (that) carriers flying. I don't pretend to fully understand some of the details, but get the gist as Delta pilots are being squeezed by both the lower end flying (understood to be ACM or feeder flying by contractors) and at the international end, by partner airlines working in conjunction with Delta (commonly known as "Sky Team") the marketing group that connects Delta with approx 20 other airlines.

Two points relative to all pilots flying under US flag rules and (when unionized) the National Mediation Board (NMB). Macro issues regarding unionization in the US have put all labor, when operating under a union contract, under great disadvantage vis their employer.
The NMB, operating under direct influence of both the White House and Congress has the power to stimie any attempt to use a work action to threaten or force any company (operating under the Railway Labor Act). The government has allowed pilot groups to strike, but only in recent years by carriers very small and (IMHO) with weak pilots groups who could not reasonably be expected to have much affect on their own pay and benefits, let alone have a positive impact on the industry.

Speaking directly to scope issues. Major airlines have exploited post BK contacts to allow ever increasing size of contract flying (both the number and size of the aircraft) by airlines not employed by the main airline. These pilots, working for sub par organizations, lack the means to affectively fight for better terms and conditions. But it gets even better. The larger airlines, not just content to have a lower cost feed to help boost their hubs from smaller markets, they contract with multiple airlines, forcing them to compete for the business, which, in turn, force their employees to accept poorer pay and benefits or risk loosing business to a competitor that is willing to fly for less (whip sawing).

On the other end of the flying pyramid, airlines are negotiating deals with their partner airlines, sharing seats, code sharing flights; so you think your booking a flight to, say, Paris on Delta or American, but in reality it is flown by Air France or British Airways. So why is this flying going to foreign airlines when, rightfully, US crews should have at least their passengers flying. I believe because pilots flying for airlines in the UK, France and Germany must look after their interests, otherwise those pilots will use the powers of collective labor (strike) or the power of their government(s) to pressure their airlines to look after their interests!!

There you have it. US pilots are the meat in a scope sandwich. Squeezed by Adam Smith and his magic of the free market system on the lower end, and by affective pressure by foreign pilots, governments, their airlines vis our disinterested elected officials, uncaring about working Americans but very interested in the money and influence of Wall Street and the bottom line of corporate America.

If you are young and wish to have a good career in this industry, tell your national leaders to get out of the way of the collective bargaining process of union vs management in negotiations and to push back against foreign influence; allowing you to fly between our country and the rest of the world. US airlines could give a rats @ss who does the flying, as long as its cheap and helps them make a lot of money. Speak up!!