While a major reset would inevitably discourage SOME existing high-ranked players from continuing, it may also give some a reason to return to the servers to push for a higher rank than when they left, as it would become more easy to do. At the same time, it would encourage a far greater number of newer players to push for high ranks, and likely many of these would purchase donator ranks to make this more achievable. So, from a purely economic perspective, it would be a good move for MCGamer. (More money -> more servers/gametypes -> more players. Repeat) Similarly for the community, if you care about that type of thing, many new players would expand/diversify the player base more, easily compensating for the loss of the few that may leave.
About hackers: Yes, if everyone resets, then it will become more likely that hackers will attain high ranked positions on the leaderboards. However, this shouldn't really be an issue as it would in fact make it easier for mods just to look at potentially illegit stats on the front leaderboards pages, and track hackers down that way. Anyway, hackers are always going to be there,it shouldnt really have a dramatic increase on the number/percentage of hackers on the servers.
All this "had to work" for, "time wasted" and "earn" wins.. If thats how you view playing on the servers, maybe you shouldnt be here. There's actually no point playing just to get a leaderboard position while not actually enjoying playing, you could spend such ridiculous amounts of time far better on doing something else.
Oh and btw, does anyone really think that a simple reset is ever going to stop Gravey4rd?