Lets see what I got right and wrong. BOTW Glitches fixed, correct.They didn't even fix the damn glitches when DLC 1 and 2 came out. They probably fixed them for the sequel. I think they dedicated at least a year to switching the engine completely to being built for Switch only, which is why there's an increased draw-distance. Maybe 2 more years to adding the expanded map and 3 years of story. Delay due to fixing bugs.
I know they spent alot of time on the story this time around after studying the leaked art book. They advanced the storyline of side mission characters from BOTW bigtime.
2 years worth of Map expansion, not confirmed but probably took more time than that seeing how large the game is.
3 years of story? Not really but since side missions have doubled in size then I'm partially correct.
Delay due to bugs etc? I got that right. I was pretty certain when I saw that Recall cutscene with the Master Sword in the Delay Announcement vid.