There are a few issues with these seasonal mounts in PVP:

1) There are a number of top PVPers that use their alts to climb the PVP ladder. While this may not inherently be an issue, it becomes an issue when those alts take up space in the top 100 that get rewarded those mounts. If these mounts were awarded one mount per account, that would help out. From someone who's tried to climb for several seasons, it is discouraging going to the PVP scene, and people saying "this person has X number of alts in top 100"

2) Getting into PVP and maintaining the ladder is pretty hard to enter. Since the PVP community is so small, from my experience, you have to rank up as soon as the season starts. If you start at a later date, half way through the season or some other, the queue times are nearly impossible to obtain. Once the DC's PVPers have gotten past a certain rank as a collective, you'll sit in over 60min queues or longer and still find nothing. It makes it slightly harder to juggle other content and pvp. There would be seasons where I tried to start late into the season, as other things too priority, and I could never get a single queue. So how is one suppose to climb the ladder in that sort of situation?

3) Win trading has been an issue in the past. When I did try to climb the ladder, again I was greatly discouraged whenever I would queue and find myself paired up with win traders. You'd have someone afk at spawn and cause a 4v3 situation. When I was playing, this felt like it was never addressed or corrected. So I could be trying my best to improve my PVP game, climb the ladder and everything else, but all it took was several of games of win traders to tarnish that.

Having done ultimate raids, I understand keeping certain content to be limited and not available to all persons. Had the Lv70 ultimates become unsync and slightly easier for people to clear, I'd be pretty upset that a fight that I've worked so hard to prog for, was made easy and thus diminish the time and work I put in for my reward. However comparing this to PVP is nearly apples to oranges, as while the philosophy may be similar, the systems are pretty different. Hopefully the points above illustrate how one sided the system is when these seasonal mounts are rewarded. In the current way of PVP, to my understanding if you want to get anywhere when climbing the ladder, you have to hit the floor running when the season starts or else you'll get left behind and climbing the ladder will soon not be a possibility. This sort of thing doesn't really happen with PVE content.