Would a reel mower cut through brambles I outher stuff that's is thinker than grass

They make cable style ones that can cut through 1 1/2 inch brush. Also there is equiptment called a brushhog that is meant for clearing away brush as a specific task. What is it your trying to do and how much land are you looking to clear ?

I doubt it.
Even some spindly weeds in the lawn would not mow down the last time I had a reel mower.
Maybe it's all a matter of sharpness. Back before power mowers they did very well on golf courses and public parks. Of course there were usually rows of mowers in tandem.