Reflectors are better because Less expensive - only have to polish one surface and don't needpure flawless glass as for refractor lens. Less sagging - can support mirror on back surface. For refractor can only support lens at its edges. Refractors have a problem called chromatic aberration - see book. Now astronomers spend great effort trying to build bigger and bigger telescopes.
Bigger telescopes give better light gathering power.
In fact we often describe telescopes primarily by their diameter. Collecting photons with a telescope is like gathering raindrops in a bucket. Want biggest bucket. Now you have learned equations. 10 M telescope in Hawaii Keck has twice the diameter so 4X the collecting area.