IMHO majors are NOT more powerful or important than minors. This is because Tarot is a system, and I view the majors as representing universal themes & concepts AND most importantly "an overall approach" to life. Whereas the minors can be used to bring those themes down into the practical arena, to show us HOW they operate in daily events.
Leastways, thats the distinction i see between the 2 Arcana's.
Tho I do tend to think of the Majors as representing greater forces @ work .. tho NOT especially things we have no control over. But rather i tend to think of the Majors as a sign that we are being subjected to our destiny.
The minors on the other hand, and as someone else pointed out in another thread, can show us details & aspects of whatever the Major signifies. So the minors are indications of HOW the energies present in the Majors will interact/unfold/manifest.
Also IMHO the minors aren't any more OR less changeable than the Majors, given that the whole point of tarot is to try and use the card(s) to gain insight, so that we may USE the knowledge we gain in a positive way .. which at times may require us to make changes!! (Tho there might be the odd "exception" such as the card of justice, given that it can be read to imply: that things out of balance will be brought into balance on a cosmic (or legal) scale). [<< info. supplied courtesy of Thirteen].
I've also noted when reading thru previous posts where a lot of people appear to think in terms of the minors as representing the more mundane aspects of life. However, I do not share this opinion, as the minors may literally show us how the themes/energies in the majors operate in our daily lives ..& if you consider some of the concepts contained in the minors .. for eg. things like failure & defeat, these may be powerful cards in themelves.
So for me the important thing about the Majors is that they appear as SIGNS that we are/have or are about to become subjected to "something". However this something/(our destiny), does not always have to be earth shattering, so @ times the emphasis of the reading might indicate that whats truly important about the Major concerns an approach which should be followed (or avoided). For instance, IF the Major occupies the advice position of a spread &/or when the Minors are clearly showing WHAT lies in store for the querent.
& As far as our being subject to our destiny to some degree, I think the emphasis here is NOT that we have no control over our destiny, but rather that @ times we may have "little control" in this regard. One example is physical illness, where altho we have followed the doctor's orders & otherwise taken care of ourselves, we may still be subject to the common cold.
Hmmn ... majors as a sign that we are being subjected to our destiny .. YET I don't view majors are being more powerful or important than the minors ... hmmn, as I say, i guess it all comes down to the importance one places on destiny .. or rather should, the importance of the querents destiny @ the time of the reading.