That's where people like the good folks at MekTek come in, if only they'd get the idea to do it, and the time to carry the idea out. Already they've got new Jump Jets in the works that will let Mechs literally fly around, and one video they showed of those in action showed the Mech in question fighting dropships.
At one time I read about a certain type of dropship that was fitted out as you describe, but with a very light complement of anti-capital weaponry. Some were even disguised as commercial ships. I believe this is called a 'Q-ship'.