Kurt Warner got his start in arena football, long with a lot of prayer, and look where it got him...
IIRC, Warner cut his teeth in the now defunct Europeon NFL, where the talent pool was lower than arena football.
Warner did use the Arena league as a stepping stone to a chance in the NFL, and he made the most of it. What is Tebow supposed to use the Arena league as a stepping stone to? The NFL? He's already had his chance and shown he's deficient in the talent necessary to be a pro-level QB. The Canadian League? With their three downs and the wider and longer field it's more pass dependent than the NFL is and Tebow is not a passing QB. Any Canadian team that picked him up would have to totally rebuild their offense around him, and having done that there is no real evidence that Tebow would be able to deliver.
The Arena league for Tebow would be a last chance to be in football at some level. There is no 'up' from there, only down to the Lingerie league or semi-pro.