Billy Schroeder was with the packers in 94 (Practice Squad), Patriots in 95, broken foot-perhaps during a lost 1996, then Rhein Fire in 97 before making the '97 Packers active roster. That year he appeared in 15 games on special teams. In 98 he had the "breakout season" to which you refer. An article on him mentions he was active for 2 playoff games after Sharpe's injury. So 5 year career, 4 years on rosters, 17 games and 33 catches.
Janis approaches Year 4, and has appeared in 35 games after 3 full years on a roster. Despite being a better special teams player immediately, he has 17 catches so far. Double the number of active games, half the production so far.
Still, he is young and is/was raw. He might still elevate his game. But he seems to be developing slower than Schroeder.
I am not condemning Davis to a fate worse than Schroeder, he is still within the normal 3 year WR window.