Here're details of my experience from just over a month ago on Delta1 and Prestige.

• Door close ~20 minutes past scheduled departure. IMHO, this is DL operating inefficiently by design. My final destination was KUL after ICN. KUL requires proof of vaccination and there's a specific app for that. Very well published publicly, the app having been poorly designed and developed is a different issue. ICN doesn't have any such requirements for transit. Neither require tests. Spent about 5 minutes on just the KUL vaccine verification as the agent didn't know what was/wasn't needed. Finally got a colleague to help, verified my status on the app and completed check-in and bag drop. At the gate, agents repeatedly announced the need to check travel boarding eligibility because of covid protocols and anyone without a blue sticker on their BP won't be allowed to board. There was crowd/queue/mass around the counter as I boarded. Guessing that might have contributed to the slight delay.
• Wait a while for pushback then stops and gos on the tarmac, just over 20m before wheels up. Was expecting to miss my connection at that point. Thankfully, several stretches with tailwinds along the way and only a couple of headwinds. That helped.
• At the ICN gate 15m from KE761 scheduled departure. Staff waiting right off the jetbridge with signs as expected. There were 5 names on the sign but after a few minutes of 4 of us waiting, we left. Agent asked us to run and she did too. Got us to head of line for security and to gate with a couple of minutes to spare. We were lucky the gate was just off the security check. Of course, it took another 20+ minutes after I got seated before door close. Ground staff repeated multiple times our checked luggage might not make it given we were late but I figured the extra 20 minutes or so was more than enough for them to move my bag. I've done one of these with gate to gate on BR in 12m and they got my bag onboard.
• Arrived at KUL to another sign with mine and a couple other passenger names. Turns out my bag didn't make it after all. Handed an envelope with local currency equivalent of about 100USD courtesy of KE and a sheet with directions to file a missing bag report. Took just over an hour to sort that out. Check my DL app multiple times and it says my bag is expedited from SEA. Weird. Turns out, mine and other pax bags never left SEA (2 of us in Delta 1 and another in coach). We arrived near midnight Friday in KUL, my bag finally arrived 1am Wed. No response from DL over "contact us" via app and website. Phone waits were hours and callback never came. ... DL? Couldn't even report loss of luggage inquiry via DL site/app because they require a report number from the local station but DL has no presence in KUL and they won't take the KE report number. Again, ... DL?

So if you're thinking about this route, I suggest avoiding it unless there's no other option or you got a screaming deal and will be fine with delays. In fact, I'd avoid any itinerary that starts with DL and ends with a partner but DL has no physical presence at the final destination.