Power per CC is the wrong way of looking at it. A 250cc displacement two stroke is still much lighter and more compact than a 250cc four stroke engine so you want to focus on power per weight.

The cost argument probably is the main driver for yard tools (Honda makes a great 4 stroke string trimmer for instance) but Endurocross bikes, trials bikes, and mountain snowmobiles especially still use two strokes for the power to weight advantage. The BRP snow machines even have direct injection which really helps emissions, though obviously they still have total loss lubrication so they're dirtier than a four stroke.