Thank you for your quick answer. That's quite reassuring, as I am currently very late, still leveling though Legion content, and I really like to take my time !
Anyway, grinding through 5 prestige levels is daunting...
And, even if they are not resetting pvp prestige ranks between seasons (btw, has Blizzard explicitely declared that? and if so, where ?) we can expect these pet rewards (4 so far...) will disappear at the beginning of the next expansion... so if we want to *catch them all*, we are condemned to daily pvp duties during the whole course of Legion expansion. And if 2 new pets are added at EACH of 6 expected pvp seasons...that means 30x2 prestige levels, omg.
I'm not thrilled....!