Explicitly telling students up front that they will probably need 5-6 years for a nominally 4-year degree program may be a tough sell, even though lots of college students actually do take 5-6 years to complete a nominally 4-year degree (even though they may have thought that they were going to take 4 years when they started).
The college telling the admitted high school senior from a weak K-12 district that s/he will probably need more than 4 years may be being honest about it, but the high school senior may see that as more of an insult and choose a different college that does not say that – even though that same student at the other college is similarly likely to need more than 4 years.