I'll add a little to this, though I'm actually from the German Version, our issues over there are mostly the same.
First of all Pay to Win has been an issue since I started that game, back when OnsOn still owned Fiesta, they claimed, that they would actually do something about it. And then the 135 cap came ... Terrible thing, I guess they know for themselves how much they messed up, since a few hotfixes here and there were out rather quickly. But still, this content is absolutely unplayable for me. I think it's ok if we can buy stuff to get certain advantages, but the content should be playable without, when there is a proper group.
The account sharing issue could be fixed rather easily, just rework the exp system - it's been a rumour going around since I started playing, which was 6 or 7 years ago, that there will be a rework soon. Well, didn't really happen, I guess. But not punishing players for grouping up, but instead maybe even rewarding them, just by a 1% exp gain, would be something for a start. Just giving 1% additional exp, per member of a group is just enough to make a player feel positive about taking someone in, and not enough, to make it worth to intentionally log in multiple accounts for the boost. Cap it at 5% so the system doesn't get abused with expedition groups. Currently the only reward you get for taking additional members in your group, is that they won't steal your mobs for it, but might steal your drops, which is another point. Just make questdrops not available for the whole group. It would be a rather easy fix, to check which quests tend to be kept, in order to enhance the droprate, I don't know the english names for the common quests so I won't name any here. But changing most of the drop quests to kill quests was a good step, but it wasn't enough. Raise the exp for the affected quests, so players don't feel punished at this point. And take away the possibility to drop for others. Of course the drops shouldn't fall only for the person who killed the mob, but randomly for a member of the group with the quest, same goes for herbs, mushrooms etc. it already works with a certain type of group bug, so it should be possible to make it a feature instead of a bug. That way you would cut down a ton of account sharing and therefore reduce the number of "hacks". Pair it with two factor authentication as already suggested and suddenly your support has a lot less to worry about.
I won't get started on the cash shop fails that continue to amaze me, but I've got an overall suggestion: Adapt to a changing world. Update your info on marketing, to rework the cash shop, and update your knowledge on gamedesign and related psychology, maybe even anthropology. This game is cut for an asian audience ten years ago. But your players are europeans and americans today in the age of about 20 to 55 - yes there are a bunch of younger and older players, but I'm talking about the majority here, which is based on my observation over the years, on the german servers, not really representative for all four versions, but I since I saw your survey I guess your office has never seen a social scientist, so my guess might be the most professional you'll get. And there are quite obvious reasons, why this game applies to this particular set of people, but I won't go into that any further at this point. Just realize that your target group is not static, they are human beings in a changing world. Just start doing your homework.