Bortles isn't perfect. That's why he was available to the Rams at an affordable price. He is better than the vast majority of backup QBs who aren't recent high draft picks just waiting for their chance. He took a tiny contract (by NFL standards) specifically to see what he could learn from the Rams.
They will need somebody else next season, but he is arguably the best backup the Rams have had in years, and frankly after some more training with the Rams, is likely going to be better than at least some starters in the league. That's why he took the small contract in an expensive place to live - to build up his value to become a starter again.