I mean, Housing First isn't based on hearsay, it's based on evidence. The Linear model is also evidence based and both have drawbacks. I don't think one can accurately state that housing first flat out doesn't work. (INB4 Cicero house study, so poorly conducted I can't handle it)

I reckon the greatest hurdle is funding. These programs cost a shit load of money, and our leaders choose to spend it on other things, same as any funding issue. But I'll hear you out on the greatest hurdle you see in the process