Here’s my personal experience on this. Pre pandemic, I travelled sufficiently to achieve both Star Alliance Gold / Krisflyer Elite Gold (SQ) and Oneworld Emerald / Qantas Platinum. My experience as far as op ups from Y to J were concerned:

1. As Krisflyer Gold, I was rarely upgraded on SQ, but it did happen, usually when heavily overbooked e.g. MEL-SIN during Grand Prix season, and shorter sectors like SIN-CMB, MAA-SIN, SIN-BKK. I was also upgraded once when flying LH (MUC-SIN). However note that in SQ, they will always upgrade PPS first, and as Elite Gold or Star Alliance Gold, you will always be behind PPS in upgrade priority, so currently I have zero expectations of upgrades on SQ as Krisflyer Gold.

2. As Oneworld Emerald, I was frequently upgraded on CX, QF and BA. This included long sectors like MEL-SIN on QF, SIN-LHR on BA, LHR-YYZ on BA, and also very often on CX e.g. SIN-HKG, HKG-BLR, or HKG-SIN. I was even upgraded on QR on DOH-SIN when the flight was overbooked. As Oneworld Emerald, I did expect to be upgraded occasionally, and this did happen frequently. On a related note, It was great to have OW Emerald via QF, because the QF/EK tie up meant you also had privileges on EK, including access to their amazing F lounge in the DXB A380 terminal. In general, I also found I preferred the OW lounges, including the CX, QF and JL lounges, to the Star equivalents.

These days, post pandemic, it is possible to do even CxO meetings via video so my travel is much reduced. I had to choose between Star and Oneworld. I eventually chose to stick to Star/SQ as I am Singapore based, and because there were more nonstop connections out of SIN on Star Alliance carriers. Although ex-SIN SQ fares are usually very high, there are usually good fares ex-SIN on UA, LH, TG, NH etc. But I am pretty sure I could have made Oneworld work as well, as we have good connectivity out of SIN on OW carriers including CX, JL, QF and QR.