Rant warning... sorry while i am enjoying the story over all there was one cliche that irritated me a lot because i see it over and over as if it's the only way that certain descrepencys can be explained when no one seems takes into account one of the most basic factors that changes the equation majorly and that is MAGIC IS A GAME CHANGER in the HP magical world it's possible (not likely but possible) that a family could have 10 different generations alive at the same time in real life you at most have maybe a living great great grand parent and thats about the upper limit of what is possible but in the HP magical world you could have a living great great great great great great grand parent that means that student aged population makes up a much smaller portion of a stable population and nothing says that the population is even stable to start with i get similarly annoyed when people try to fit the magical economy into the same basic mold as the muggle or real life one but there is no reason for it to be any where near the same because MAGIC IS A GAME CHANGER how much do you actually need to buy in the magical world? especially if you're any good at transfiguration you don't need to buy furniture nearly as much EX
muggle: i'm throwing a party that has more guests than i ever had before i need to buy more chairs for them to sit in
Magical: i'll just conjure or transfigure some extra chairs or a longer bench and table for everyone
see how much different that makes the furniture industry EX2 also affecting the furniture industry
muggle: crap the table broke now i need to buy a new one
Magical: Repario there we go good as new
so what was a necessity now becomes a luxury and thats just two examples ....
when crunching the numbers a lot of people forget to take into account that wizzards live longer than muggles not just powerful wizzards like dumbledor but the same person who gave dumbles his owls gave harry his that means that aside from the statistical freak that is flamel dumbles is still not the oldest living wizzard by a fair amount assuming magicals have any sort of retirement someone who was old enough to be one of dumbles teachers is still working a job not retired so you don't need as many children to have a large population if some of them just live a long long long time and who says that quiditch players only play an average of 5 years it's possible with medical magic being what it is that pro Q. players could have careers possibly in the 50 or 60 year range which would allow for many more teams from the same limited number of potential new players each year
also who says that the magical population is at all stable it could be that magical briton is at the TAIL end of a baby boom (by tail end i mean the population surge that was once a high percentage of babies is now a high percentage of old geezers) so in that way there could be student numbers that don't support the rest of the population numbers because those population numbers are going to fall sharply in the near future because there arnt enough kids to replace the dying old people
so why does pretty much every fic writer who tries to fill in the blanks of the population to class size miss match always come up with the same basic filler hogworts is big enough that it could probably have 100 times as many students and might have had such in the past so does no one come up with the alternate filler that instead of being at the start of middle of a baby boom (like the USA i believe has just gotten past the mid point of a baby boon the large generation is getting ready to retire) that they could be at the tail end of it and most of the population is old people who have already retired