Decades ago, there was a time when "direct" flights with stops truly did offer convenience. Maybe you could stay on the plane, or get off to stretch your legs but leave your stuff behind, and have a pretty short layover. I remember doing things like YYC-SLC-LAX "direct" in the 90s, and it was pretty easy.

Nowadays, the only reason these flights exist at AC* is to increase revenues by deceiving customers as to the convenience of the experience they're going to get. If people don't notice the stop, or think it's going to be a quick off and right back on the plane, they're more likely to buy or pay a higher price.

*There are some airlines where, on some routes, some of the previously mentioned conveniences do apply, e.g. on ET's OSL-ARN-ADD, it's a quick stop and through pax get to stay on the plane. Same with SQ BCN-MXP-SIN.

All "direct" flights with stops are affected.

I don't see how LHR-DEL can possibly be harder to upgrade than YYC-LHR. AC sells this as a 5th freedom route, and there are lots of people just buying LHR-DEL-LHR. Being based in the UK where AC has a much more limited presence, those passengers are much less likely to have AC status, meaning less competition for upgrades. And YYC-LHR has usually had very strong paid J demand, meaning limited supply of upgrades. Unless AC is so highly perceived in the LHR or DEL market that there's massive paid J demand, it's likely that the LHR-DEL J cabin is no more full of paid J traffic than the YYC-LHR J cabin. So, similar or greater supply of seats for upgrade, less demand = easier eUps, not harder eUps.

In the RESIII days, that may have been much more true. With Amadeus, it's a much bigger system built by a 3rd party. It might be possible in theory but not at all practical or financially worthwhile.