Clarification please:
Its not fair if dome teams cant play in a dome, because they built their team with that expectation.
---BUT---
It is fair to make outdoor/northern teams play in a dome, even though they build their teams to cope with the elements.
Is that what you're trying to say?
You say "best playing conditions" like it means the same thing for every team. Optimal conditions are relative, the Green Bay Packers would much rather play with the New Orleans Saints in a snowstorm than in a dome.