Not necessarily so ... and it's an assumption that doesn't take anything about that diver into consideration.
FWIW - I've known, and trained, some divers I would inherently trust as a dive buddy far more than some old-timers I've known. Being a good buddy has less to do with experience than it does attitude and habits.
Much the same can be said about the scenario posited in the initial post. You can't tell much, really, about a diver by looking at him. And you can't tell much about how safe he's likely to be by the gear he's using. Having a pony bottle is only worthwhile if you have the presence of mind (and the ability) to deploy it in a timely manner in an emergency. I once dived with a fellow who told me his solo strategy was to dive until his main tank runs OOA, then switch to the pony and come in. I'm sure he wasn't trained that way ... but even after I explained to him why that wasn't a very good idea he continued to not see anything wrong with it. Divers like that can't be reasoned with ... and it's best just to stay away from them and let Darwin sort it out.
The problem with people like that is that they aren't just a danger to themselves ... but to those around them. And you don't have to be someone's dive buddy to be accosted by them once they put themselves in a position to discover that they're not nearly as well-prepared for an emergency as they thought they were.
So no ... give me the new diver who paid attention to his training, and who is working hard to improve any time over the older hand who thinks he's got it all figured out and routinely cuts corners. Chances are pretty good that even in an emergency, the former will be better prepared to think their way through the emergency without creating an even bigger problem. A good attitude frequently trumps a good number of dives in that respect ...
... Bob (Grateful Diver)
I think those of us who have been diving for many years have seen all sorts of extremes, including the occasional "older hand who thinks he's got it all figured out and routinely cuts corners" to the vast number of more recently certified OW and AOW divers with the usual low level of training who have trouble putting their equipment together properly, who have great difficulty with buoyancy, flapping at the surface or bouncing off the bottom, hand clutching inflator, eyes bulging with alarm, producing a white storm of bubbles more approriate to a submarine.
So no...give me an experienced diver, an old hand who does not cut corners because their training and experience has taught them the imprudence and folly of cutting corners. My own pre-dive check list and safety checks while submerged have expanded, not contracted, over the years. I think this is true of all really good divers.
I dive often in the Caribbean, frequently in the presence of awkward new divers who seldom check their SPGs, but can blab endlessly about their SAC rates and who expect the divemaster to 'take care' of them.
I keep my distance.
More experienced divers who have a few short years under their belt but who are fools, inclined push decomp limits, to seek out and push the the most 'liberal' computers, to make risky penetration dives, to push the envelope and take stupid risks because their tiny brains interpret all this as exhilarating adventure are equally to be avoided.
In my experience a good attitude is more often the result of many dives, lots of experience, learning to depend upon one's self, understanding that there are always real dangers and that we are completely and exclusively responsible for preparing to deal with them.
Experienced, careful, skilled divers who rigorously prepare for each dive are a third category between "the new diver who payed attention to his/her (frequently superficial and inadequate) training", and the sloppy corner cutting older diver who more often than not dives infrequently. For some reason you fail to mention them, though they constitute the majority of highly experienced divers. Pity, because they are the best people to dive with.
