However, the TYPICAL new diver with jacket style BC will be swimming head up and feet down....this is pathetic as a byproduct of lazy instruction--trim "should have" been addressed and weighting perfected prior to issuance of c-card. The jacket-style bc is harder to obtain a perfect horizontal trim/swimming position, but it absolutely CAN be accomplished.
Since I have no problem producing new divers that have perfect "head slightly lower than fins" trim/swimming position in an ~24 hour PADI OW course, with my employers Mares vest BC's that I don't think are as well designed as my old SeaQuest vest BC's, I guess I could thank you for the compliment.
Instead, I will point out that there are lots of vest BC's on the market; especially if you include second hand. There are also lots of different body styles and levels of athleticism among the new divers today, and many of those "typical" new divers you see did their check out dives years ago in some quarry with 40 lbs less gut.
For the most part, humans are lazy; that's why we have invented so many "conveniences." I think it is likely the majority of dive instructors are teaching good courses and their students probably dive well on their last check out dive. Divers, being a subset of human's, are lazy for the most part, so many can't be bothered with diving well after they get certified.
Using anecdotal visual evidence of lazy divers as "proof" that all vest BC's are "harder to obtain a perfect horizontal trim/swimming position" is, well, LAZY!
