Signing Kitna is a step in the right direction, but I wonder if what they saw in Kitna was markedly better than what they saw in Josh McCown. I think the main difference is that Kitna is an established veteran and former starter who's had some success. Other than a handful of 300 yd games, McCown has not tasted success but seems to have more upside yet less polish. At this point, Kitna is the safer pick perhaps, but McCown might have been a better selection if Harrington doesn't work out under Martz' tutelage.
Speaking to the Lions moves, or lack there of so far, I don't think it matters who they line up at QB. Until they address the offensive line and upgrade their right tackle, left guard and center positions, whoever plays QB is getting fed to the Lions.