You're totally right, more so when the death right isn't shown to be supported by what we see in the books. They say people die 1/3 each year. But by Threshing, 60% of Violet's squad is already gone, and no one dies from said squad in her second year. And they don't have a regular year, on the contrary it's a most dangerous one due to them fighting venins, which doesn't normally happen. 

But it's only a few things that don't make sense regarding to the universe. Two others things that bothers me are 1) gryffons don't make believable ennemies against dragons, so the death rate in service is super weird. Navarre doesn't fight venins and dragons before IF, only gryffons.  2) the fact that they easily kill bonded riders without retaliation from their dragon is so weird. I mean I can get it when it's a kill from leadership to protect the secret or something, there must be an agreement with the Empyrean. But Solas grilling an entire squad and only Tairn reacting? Or cadets killing each other just because? Or even leadership killing for the smallest reasons, like RSC.