Certainly if the Arizona Cardinals want to go with a quarterback with one of their 11 picks in the 2019 NFL Draft, then they should go for it. However Mike Glennon should continue as the backup and if not him, then another veteran.
Whoever they draft can come in and compete for a third quarterback spot, if that is the way the Cardinals wish to go. No indication yet how many quarterbacks the Cardinals will plan to carry for the 2019 season.
Despite Glennon not setting the world on fire, he is a veteran that can continue to support Josh Rosen, the incumbent starter.