Bowl size means nothing
For efficiency? Really? Sorry, in the real world it does. Opinion yes, but consensus opinion. While it's possible to be extremely efficient with most any good convection vape, trying to get the same efficiency out of my SSV, as I do with the small bowl on the PD, is downright frustrating. It's like driving a sports car in order to get the maximum gas mileage. It's not designed for that. No fun at all. And I've seen a number of posts on various forums from people who weren't crazy about the efficiency of the 'cano. To be fair I'm not impressed, efficiency wise, with most of the vapes I've used (about a dozen) compared to the PD. It's just the best design out there for encouraging efficiency. As for proof, it's easy to see how much you're using with different vapes. I've proved to myself that the PD is king of efficiency, as has every other owner who's expressed an opinion on it. And there's a ton of owner feedback at fuckcombustion.com.

I've never tasted diluted vapor from my cano but if you're referring to the taste of leaving a whip on too long cause you want a big hit and it ends up tasting charred in seconds
Vapor from any bag is less concentrated than from a whip vape. This is commonly accepted. When people use both methods enough and/or read opinions from others who have used both, it becomes obvious what the majority opinion is.

There are strengths and weaknesses to various vape designs, and one model can't be THE BEST in all areas. Lots of people don't like bags. That eliminates the 'cano right off the bat. Others want direct draw and bag fill. Doesn't satisfy that requirement either. More and more, people who do a lot of looking around at what experienced users of multiple models are using, are finding that the Volcano is not always the popular choice. I can point you to a 'cano owner on another forum who's vape of choice is now the Purple Days. Let's just say there's lots of competition these days from vape makers who are providing different types/styles of quality vapes, and leave it at that. At least that's where I'll leave it. I'm sure you'd like to have the last word though.