What you are saying sounds sensible, but remember "we don't know what we don't know". Meaning, we are unsure of, and cannot really assess the quantity of, whatever we aren't aware of.
I just find it too big an assumption based on what we think we know about our world, and leaves off too many possibilities.
We know how OUR world has worked so far, and we can't even imagine someone less advanced than us being more advanced in a single area.
But that's just the thing - that's how OUR world has worked. It may not be the same paradigm in theirs. The whole point is they'd be different worlds, with each person probably making the mistake of using their own personal paradigm to judge another's world..
But truthfully, I was thinking more of "making contact" simply.........rather than an all-out, sophisticated space ship.
How do we know some world that's less sophisticated than ours hasn't discovered a type of communication that might reach us we don't know about?
We think very linearly, and very according to our line of linear discovery. Theirs may be surprisingly different.