If you keep winning matches, rating limit won't affect you.
If you're in G level, your rating will keep increasing over 1.400, the only difference with other countries is that you'll decrease your rating a little when you lose a match. But it doesn't mean that a G level team can not have higher rating... Besides, that limit exist to ALL countries, not only Thailand (yes, i know thai managers are a lot more than any other country).
But in the end, i believe it's fair, it keeps a balance between old and new teams, if somebody wants to reach a higher level team, he must earn it.
And yes, i know what it feels to be in a lower league, i've been here for a while and i haven't reached top level yet.