The quote from Vaykira Rabbah of course does not mean anything the likes of what you took it to mean. The medrash there states only that out of a thousand students, only one ends up being really something special. That’s true about everything — of a thousand kids who play basketball, only one will go to the NBA, of a thousand scientists only one will help cure cancer, of a thousand writers, only one will author a best-seller, v’chulei v’chulei. But chalilah that does not say anything the sorts of that which you are suggesting — that somehow it is worth our sacrificing a thousand of our children so we can get out one gadol. Chalilah v’challah.
Also, despite what’s written on that site, the Rambam never says anything about a thousand fools dying “to obtain one genuine scholar”. The Rambam does not say that in Mishne Torah, not in Peirush hasmishnayose, not his tshuvose, or any other of his ksavim. What the Rambam does say, in the psicha to Moreh Nevuchim, is that he prefers to address the one wise person, even if 10,000 ignorant people will fail to understand him. Of course the meaning there is unrelated to what you are suggesting.
Finally, of course there are yeshivas that will not push out general slackers, but will push out those studying in college. Some have something against college per se. But of course any serious yeshiva will not allow a bochur to stay if he spends half his time selling things on ebay, etc, any more than if he were in college. I’m sure there is no serious place like this that would be ok with a bochur spending serious time on outside pursuits. Small jobs here and there people are usually ok with since it might provide a small parnassah, it’s a good outlet, etc, but not a distraction from one’s growth. College, just like any other pursuit that requires substantial investment of time and effort, would certainly be a problem. And yes, there are yeshivas that do not accept married bochrim, in large part because that detracts them from their learning and hasmadah.