I don't think any team in the NFL has somebody on the bench at left tackle who could have just jumped in there during a playoff game and not missed a beat on that side against that defense. There aren't enough blue chippers at that spot as starters in the league, much less as depth. And, even if you do have a serviceable replacement, it's unlikely they'll have exactly the same set of skills as your starter, which means your protection schemes have to somehow adjust on the fly.
Doesn't mean Free doesn't necessarily have the tools to play that spot (or can't in the future), just means that he's no Flo, and there was no way he (or pretty much anybody in his position) could have been completely ready for that moment.
Then, you combine that with Free also being the guy who should have spelled a rusty Colombo at RT, and the mess you traditionally get when an OL unit (that's essentially played together all year) gets rearranged, and it's recipe for disaster either way.