Depends on what you call training. 250 hours under a private (no payment allowed) licence, then you get your CPL. All of this is on your dime (average about $200/hr with instructor and such). The CPL phase work afterward (banner flying, flight instruction, etc) pays like garbage since the GA community is struggling significantly. To do airline work, you need minimum 1500 hours (ATP), then pilots have a sort of residency beyond that where they need to spend a month in airline training, then years as a first officer before becoming a captain (PIC). On top of this, you have the regionals where you get payed like crap before you can typically get a seat at a major airline.

Doctors begin their professional training after 7 or 8 years of post secondary education.

Much of the time, on their own dime.

They also generally work hard enough in high school to get excellent grades (do flight instructors check transcripts or just if the check clears?).

It's easy to imagine doing 250 hours over 3 or 4 years while doing something else most of the time.

To fly for the airlines you'll need a college degree, probably with a >3.0 GPA. I agree it's not as academically rigorous though (unless you count the USAF route). Also, most people I've seen do the 250 in as short a time as possible or go part 141 which is a sort of direct-to-CPL training program. Right now there's a shortage of airline pilots but traditionally, those 7-8 years you mention would be spent at a regional before you have a chance at making enough money to start to really service all the debt you undoubtedly have at that point.

Obviously they're pretty different career paths, but they're both effectively 'trades', in a more traditional sense, that require obscene amounts of training.

Pilot pay SUCKS though. Even once they reach the airlines new pilots are only making about $30k/yr.