I understand the issue, however, after reading Zaku's comment, I don't think it is quite as you described.
Even ignoring that, from the poster's point of view, bdvoter is giving us a nice upvote, bigger than any other upvote for most of us. On the other side, there's someone who we don't know and have never seen give us a single upvote, who just downvotes our posts without any explanation. We had to find out the explanation ourselves and it honestly doesn't get better after knowing the reasons. This type of stuff is done by people who earn more hive than most Splinterlands players combined.
Anyway, I don't think this is an exploit by Zaku, nor something the Splinterlands team can easily fix, unless they moved from manual curation to automatic curation, which would have several different problems. It's more of a problem of the system. Even if you believe Zaku is exploiting the system, getting a higher APR from their voting and Splinterlands getting a lower APR, this is a 0 sum game. Splinterlands lost out, Zaku won. The DV now hurts Zaku but also hurts Splinterlands and all other voters, and hurts the content creator the most. Why not give a similar-sized upvote on a post or comment to compensate for the downvote?
And I don't understand the "additional sell pressure on hive". Any hive earned can be used for whatever we want. If we want to convert to HBD that's ok, if we want to power up to have more hive power is also fine, but so using that hive to buy some other token or even get crypto from other chains or fiat. This part should have no influence on the decision. Would it be ok if I stole 500k hive and just didn't sell? Would it not be ok if someone earned 500k hive legitimately and sold?
That's up to @marky, splinterlands could also just upvote a comment to prevent rewarding sniping taking half of their returns.
It is what it is, it's easy to try and find reasons to side with the person rewarding you so this comment is quite loaded. I personally think it's quite disgusting to take advantage of how the blockchain works to take rewards from a project that has carried the chain forward in many ways for your own gain, especially when they are struggling and then pretend like they didn't know any better.
If they didn't want to continue doing this they could just trail splinterlands to vote at the same time/on the same day as them so the rewards would be equally shared among them.