True but I think the article's point was that you could maintain the same professor-student ratio and increase class sizes if you have the billlions that Harvard had. Instead they spent the money to make them seem more prestigious.
You could maintain the same professor-student ratio, but you wouldn't be able to retain the same professors. If Harvard expanded, it would be less able to maintain the 'superstar professor'-professor ratio because other colleges would be able to court the professors away with offers of greater access to better facilities and bigger corner offices with better grad student support.