HUDs are a supplement, not a substitute. You still need to observe and think. Sure, you have rec players whose game hasn't changed in 20 years. You also need to be aware if something's changed. On one site, I had a regular whose game was pretty solid, but once or twice a week his game just fell apart. It was like playing a whole 'nother player, and I think that was what was happening: he was letting someone else play his account. That tainted his HUD stats (maybe why he did this?) If relying too much on a HUD, you'd miss that, and miss the opportunity to take advantage of the weaker play.
The other problem is that its stats aren't of much value until you have a significant sample of hands, but by the time you do, that earlier data is getting stale. How he played in the past may not reflect how he plays now.
There's no substitute for observing and paying attention to what's going on around you.