A convex edge is best for two reasons.
The first is because we are all just human and we are not robots, the second is because we use what tools we find best and easiest and we are not using the grinders used to sharpen the knives at the factory so we have to work with what we have.
If you look at a factory edge you will see it is very rough along to bevel, you can easily seee the grind marks. These edges are put on by a machine (or often by hand) grinding those edges against a paper wheel or a massive stone wheel. They do it in one or two quick cuts each side and ship it out. It produces an edge that is ever so finely hollow. The problem for most people is when they get home they are trying to replicate this same edge and it is just not as easy as it seems. Nobody can hand hone a knife and keep the angle so perfect that they are always touching the edge and the heal of the edge bevel at the same pressure, maintaining the exact angle between the two for the length of the blade. You certainly can't replicate the factory angle with your flat stone, it is hollow to begin with and you are flattening it out. Almost all the time the edge is taking the beating and the shoulder isn't, thus making what came as maybe a 25 or 30 degree bevel something like a 40 degree bevel. face it, how often have you sharpened you near new knife and been upset because you can't get it to shave like it did from the factory
You can do better, you just have to accept that your knife isn't new any more and you need to remove steel. You can buy a Lansky or similar and keep your shoulder looking fine, but still not factory new, and persist with the idea of a perfectly flat final bevel. This is where us not being robots comes in. If you use a steel on your knife later (you know you will) the shoulder will force you to angle the blade exactly, either you will be steeling the shoulder, or you will be steeling the edge, and we know which will give up material first, the edge. As soon as you put the steel to use you end up with a courser angle to your edge.
Or you can ditch the factory edge right from the start. Take the shoulder off so there isn't a sharp transition from grind to edge bevel. This gives you some fudge room to allow you to be imprecise with your sharpening and not keep the exact same angle all the way through the sharpening of your blade, you just have to think about how much pressure you put in to the edge.
Ditch the shoulder, use a strop and watch what you thought was an okay blade become a hair poppingly sharp blade.
I could not get through to him that a softer blade of good quality might suit him better as he might be able to sharpen it himself.There is a def plus in a softer blade as you can sort of steel it on any hard smooth edge surface.I have even herd that you can use the top edge of the window on the car door.I agree that a good blade should be able to do a whole deer size animal without attention but not many of use get enough practice in the job so cut a bit more hair and bone than we should.I made a bit of a blade this week and was working on the handle section so the blade was wrapped it masking tap but dropped blade and it landed on its tip on the cement floor. 
It took me 10 mins to get game enough to take the tape off but to my suprise only the tinnyest deforming of the tip,no bend no broken tip so I must have got the heat treat just right on that one I guess. 
(Better to be lucky than good)..
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