I believe you are. I would be surprised if it was even 10% of people who would prefer the Tamron. Let's just pretend everyone (on this forum) wins a free lens at the camera store and they have a pile of Tamrons and a pile of Canons. I really really really doubt that given the choice, very many people are going to walk out with the Tamron. Because I deal with contracts and by nature, "paranoid", I would even say that the choice would not change much if you told them they could not sell the lens.
The point I am making is that I believe the 2 canons are the best but the tamron is very close behind and will give you undiferentiaded results under most conditions so anyone on a budget should take a good look at it.
Anyone on a budget doesn't have a choice but to choose the Tamron. Someone with (truly) the budget, is going to pick the Canon (nine times out of 10).
In that case I must be in a minority of 1 out 10. If you have the strength and like using monopods or tripods then go for the Canons if you have the cash - you will get the ultimate quality. But, if you want to use hand held and like a light package for hiking and birds in flight etc, then those great lenses are just too heavy. I could not handle them. I would rush out and buy a Canon 200-500 f/5.6 that beats the Tamron, and pay the price.
You might as well ask suppose somebody offered you a 100 carat diamond studded solid gold mounted Sigma 50-500 or a plain Canon, which one would they take? That situation is just as unlikely as everyone on this forum being offered what you would suggest. If I was given a 200-400mm Canon I would never use it. And that is a fact, not a let's pretend scenario. But, if someone were to offer me a 200-400mm free of charge, I would of course accept it - that is human nature.
The point in question is whether the Tamron or Canon is preferred, ceteris paribus.
The only reasons I can imagine for buying the Tamron over the Canon are price and weight/size. You already said you don't want a big lens so you've explained that your utility formula places a higher value on size/weight. Because this forum is full of gearheads and guys who care about IQ, I still believe that at least 90% of those on this forum would choose the Canon over the Tamron if they could afford it.
You can go buy the Tamron.