^ Did airlines really book you on a rival airline, when flights were cancelled?
11 years ago I had a CX flight which was canned, but the alternates were One World … VA can only really stick you on their competitor‘s flights if they run out of flights themselves.
They can, it depends on a few things, and the other airline needs to have an interline agreement in place. They'll still try to rebook on their own or partner flights before going to another unrelated airline.
eg, if Qantas has a problem on their US flights, they'll try to reroute you to another QF flight from another city, then go to AA, then to JQ/AA via HNL or FJ via NAN. If that doesn't work, they'll try CX or JL before going to NZ or another US carrier.
Qantas can rebook you to DL or UA, but it will be their last option.
Some years ago, I was booked CBR-SYD-TYO. There was weather issues in SYD which kept delaying my flight out of CBR. When I went to the ground staff about the delays, they said they'd put me on the next flight, until I pointed out that I had an international connection. At which point they went "oh cough" and started to work on rebooking me. JL was booked out, both the flight that night out of MEL and the SYD flight the next morning.
They decided to get me to MEL, and their first choice was JQ to NRT via DRW and MNL. I wasn't going to take an A320 Y seat with 2 transfers in the middle of the night for a paid W seat with J opup. They ended up putting me on CX (who opuped me to J the moment I walked into the CX MEL lounge).
My last trip in 2019 started with CBR-MEL-xSIN-HND. I got to MEL without issue, but the aircraft meant for the MEL-SIN had been hit by lightening on the inbound and was delayed and then cancelled. Everyone else on the flight was rebooked to the EK MEL-SIN-DXB flight. If I'd been moved to that, I still would have made my connection to JL. But QF wouldn't do that, refusing to move me to EK because I was on a oneworld ticket (even though they were allowed to use non oneworld airlines in such events). They had me go backwards through immigration, sent up to SYD then on to QF25.