You don't develop on the bench, I have no idea why this is even a narrative. What current starting QB can you point to that sat and "developed" for a year or two? Mahomes? Chiefs were a playoff team his rookie year. Hurts? Eagles made the playoffs the year before. Jordan Love? 1st ballot HOFer in front of him. Of course none of them are going to start immediately, but everybody else was pretty much handed the keys from day one or at least starting before their rookie season ended. If practice reps were so valuable, then all these career backup QBs wouldn't look so lost when the starter gets injured.
Richardson's #1 issue is accuracy. He's got an above average deep ball, especially on vertical routes, but crossing routes in the short to intermediate give him trouble. Part of that is timing and quick decision making given the dynamic of Steichen's scheme, but you're not going to improve on that simply getting practice reps especially vs. our vanilla a$$ defense.
All that to say, it doesn't make anymore sense to bench him than it does to leave him out there. We're not contenders with Flacco either way, sure we might win a few more games, but we're not making any noise in the playoffs no matter who's under center. So what's the point? It's gonna be ugly, especially with the teams we're playing the next few weeks. But we used the #4 pick on him and we're not a true playoff team, so you gotta ride it out at least until his rookie deal is up