I don't know what powers does, but hipow should be
in the system, as well as coef and ratcoef .
I don't know about expanding, but typically ratexpand is
much faster than expand, and there is probably no way
of computing ALL the powers without expansion. If you
want only the highest power, it is possible to do so,
but in the worst case you would have to do as much work.
Proof.
f(y)*x^10 + x^9.
The highest power of x is either 10 or 9, depending on
whether f(y) is 0 or not. How can you tell? Expand f(y) etc.
RJF