Playthrough #1 (Hard)
I stumbled across a comment somewhere containing a link to a video of a streamer completing OW1 in like 30 minutes so I copied what he did and finished it in around 4 hours on hard difficulty in early June. The key is to shoot the main npc quest givers in the head, nullifying entire arcs of the story and moving you forward to the next one.
I just had Parvati as my companion and had to heal a lot but managed it fine. I didn't even have to shoot a single shot in the final area.
Playthrough #2 (Supernova)
A week later in mid-June I booted the game up again on Supernova difficulty. I died a lot but took my time and grinded here and there and it was not too difficult. Lots of dying but the limited saves attached to this difficulty was not too hard to manipulate.
Playthrough #3 (Normal/DLCs)
After completing it on Supernova, I played it again the next day on Normal difficulty. So much easier. I also skipped a lot of the missions by assassinating the major NPCs but also had to stop and grind experience as I planned to do both of the DLCs.
The Gorgon DLC was decent, a bit too dark and lonely for my liking. It needed a few more interesting people to talk to.
The Eridanos DLC was better, I enjoyed the whole murder investigation angle.
Afterward all I had left to do was the 50 stealth kills achievement. I got that in a few minutes after re-speccing as a stealth sniper. That was actually a lot of fun, almost wished I had done it earlier. I can always get the enhanced edition if I want to get all the achievements again.