The thing to keep in mind is that your technology should always been advanced in proportion to all the other Tiers. Unless you undergo some serious nation reform (like a massive population drop).
So really, if you are Tier 5, you should never really have better technology than (say) Tier 3 nation unless you were give some kind of really good deal by a Tier 1 nation. Or unless the Tier 3 nation stagnates and does nothing for 3 years or something.
Its not all that clear-cut I guess, but the main point is to avoid a scenario where suddenly 250,000 tribals are armed with power armor and plasma weapons and suddenly no-one can stop them.