[PubQ] New (?) submission timelines

My agent is taking my book out on sub in the next week or so, and I’ve been watching YouTube videos about things authors wish they knew before going on sub. One video from ~3 years ago, from a Middle Grade Fantasy author, said that she’d had no idea how fast editors would respond in comparison to agents. She said that within a week of being on sub, she had responses from 15 out of the 17 editors in the first batch.

I know every sub story is different, but that’s just mind-boggling to me. Is this at all a common thing nowadays, or more of a rarity? I also heard that sub varies by season, and summer is notoriously slow.