There's absolutely no way AGC picks that up especially at your ping. I doubt any anti-cheat is capable of picking that up.
Just because he has reach enabled doesn't mean he will always hit above 3.0
And "10 pages of logs" would probably result in him either being frozen/auto-banned/ban-waved...
You can continue using it, toggling isn’t necessary. As I said, I doubt Hypixel has a check for KeepSprint; they focus on patching the more prominent cheats.
Some servers can have the slowdown you experience due to sprint disabled, but most don’t.
It’s extremely detectable if you think about it, you can just check if player slows down after attacking or continues at the same speed. I doubt Hypixel has this check as they usually focus on patching...