Drifitng proves that you can slide a car around a track. It doesn't prove anything else.

Dyno=You have to build a good motor to make good numbers.
Drag=You have to build a good motor to withstand racing, you have to make good numebrs to run good times, you have to drive well to get a good time, you have the car setup well for the best possible time.

Show=proves you can waste a lot of moeny to make a car a useless piece of shit. Wow, you spent a $120k on your Civic for doors and hoods that open the wrong way. It doesn't prove anything for a performance shop. No real performance shop should even deal with bodywork and that crap.

Drifting might be more fun to watch for some people, but it doesn't prove your abilities as a shop.