For the average joe a poly lower is fine.
This has to be the most underrated put down on the internet. Please don't think I'm singling you out because I'm not. But I see it everywhere, the idea that if all you do is shoot bullets out of a gun, then that is probably good enough but yet some how not recommended either.
When it comes to 3-gun, you will see a variety of equipment and plenty of it is not gun forum approved. Honestly 3-gun is harder on optics than it is on guns IMHO. Almost all 3-gunners shoot at the local level, do it recreationally and don't have the budgets to run the most highly recommend setups. I mean I use a pre-ranch Mini, a Winchester 1300 and my $1000+ 1911 because I am serious about USPSA but 3-gun is a side thing for weekends where I'd have nothing else to shoot. I'm sure I will eventually see poly lowers at competitions. I already see DPMS and Bushmasters right along with Scars and Noveskes.