Well...sure Watson was only 23 in 2018.
Mahomes and Wilson aside...Watson is so much younger than those guys when they became the players we now know. A 27 year-old Watson could be a much scarier opponent...especially if you have a motivated BB coaching him.
No guarantees of course...but I am only taking a handful of QBs on my team over Watson right now. And as much as I was onboard with Rivers (even before he signed)...Rivers isn't one of those QBs. The Colts can still win with him though...but the margin for error won't be there.