Not sure about instructor route either, know many good instructors who never made it to airlines. Don't see how instructing experience on C152 makes you better turboprop/jet pilot. Completely different environments.
Who would you choose?
- An instructor who has 1000 TT
- Someone who finished training 6 months ago but is just sitting on his 200 TT expecting a job to fall into his lap
Not all instructors want to fly for airlines, instructing is a perfectly decent career. Also saying more experience on a C152 won't make you better than someone with less experience is a bit strange. With your line of thought wouldn't it be pointless in training full stop because training is done in light aircraft, and flying light aircraft doesn't make you a better pilot?
Airlines have minimum hour requirements and not all of them require heavy aircraft time, so instructing is a good way to get those hours.