If you think too much of an account being an alt, I can assure you that you will do more evil than good, many genuine and original posters must have been discouraged because of this and left. While you make the forum thrive for alts simply because they with the alts must have understood the forum better, and whether you give them or not, they get it elsewhere. Is that justice?
Take me as an example, I am no alt, but I would have left the forum in the first 5 months if not for @The Sceptical Chymist, his support encouraged me. @JayJuanGee is another good and random reviewer who I wouldn't have known if not for the merits he sends to me. How many people do this? My discouragement at that time is about the lack of appreciation of what I contribute, it goes a long way.
Mind you, Injustice is everywhere in the forum, and if you look at some local boards, you would be amazed about what is happening there. Some underserving accounts could get as much as over 300 merits in a single month, all local. This is simply because they can speak their language, many might have alts there and continue to build it for money, is that justice?
I implore anyone God has given the grace and privilege to hold a position of power to help regardless of discouragement by anyone, JUST BE YOU. It's not so difficult to read posts insightfully and psychologically to know who deserves merit and some suspected alts. That's at least for me.
You make quite a few good points, and probably I agree with your overall conclusion regarding various difficult balances that may well not even lead to any kind of system that is even close to perfect, because even if theymos might make some kind of change in regards to the number of merit sources and merits, but then some of the merits might end up getting spent in ways that really had not been what was intended buy the change(s)....
and so frequently, I mention that theymos might want to do some juggling of the merit source members, and he does do that from time to time (but pretty infrequently), and maybe part of the reason that he does not juggle too frequently is that it may well take quite a long time to figure out the various kinds of fall outs that might occur each time the juggling might have had been in a kind of BIG way...
Merit czars had been suggested too.. and sure that sounds good in theory.. but likely would have quite a few negative aspects too.. even though i would imagine that theymos does have some names of members that he would calculate to be less likely towards corruption as compared to others.. but everyone likely has some flaws in regards to sometimes even having time to carry out such duties... or even the right kinds of skills and access to administrative tools.. which there might be some difficulties in terms of giving some of that kind of access to administrative tools too.