I love the art - I just get irritated when I see rather obvious errors like 20 foot tall trolls and such. 
Measuring, and assuming that the human-looking fellow in the image is roughly 1.8 meters tall, it turns out that troll is roughly 3 meters tall... that doesn't actually seem all that far off of normal to me.
...though I guess that would make him 10' tall while the average troll is only 8' 2" tall according to the SR5 book.
But then, the book also says the average human is just under 5' 9" and I am 6' 3" - so if trolls experience the same degree of deviation as humans in height, then my equivalent "tallness" would make a troll 8' 10.5", and if we took the equivalent "tallness" of the troll depicted in the art and scaled it to human ranges of height, well, it's only 7' tall - not incredibly uncommon at all.
I actually think the proportions in the art are good - shows how seriously huge trolls have always been, even though the art kept depicting them as barely taller than humans.
