What you're missing is the three best players on the OL other than the starters are the OTs. There isn't a decent RG on the team so if Long struggles at RT you've compounded the problem by creating two weaknesses where you have just one.
So many have been anxious to move Long to OT, but if you've actually seen him try OT you'll realize how bad he is. Long despite his NFL Combine success is not an OT type of athlete. Long does bend well, he doesn't kick slide well, he doesn't work his way out to the edge in pass protection well as an OT needs to do.
The idea that Long can play tackle because he's 6-6 and runs a fast 40 and jumps really high in the vertical and broad jump doesn't mean that skill automatically translates well to him playing OT.
I have no idea why this simple fundamental gets lost with so many people on is board but it does, just because Long performed well at the combine and is tall doesn't mean he is the same type of OT athlete as Tyron Smith.