What are the significant assumption of the Inflation Theory? Can it still be considered theory ?, because I can't find it's major or significant assumptions.
The most significant assumption is that very shortly after the Big Bang, the universe expanded very rapidly for a short period of time. Much faster than normal expansion due to Big Bang. It was an exponential expansion and occurred around ${10}^{-32}$ seconds after Big Bang and lasted for tiny fraction of second. The universe continues to expand but not at that exponential rate. Yes it is still a theory and is accepted by many scientists.