That is not quite right. There are a lot of series that don't air late in the night. I would say that in any given period of time there are almost the same number of series running during the day as those in the night.
Toei animation earns more money from TV than Disk Sales, and even if that wasn't the case TV is highly important, because an episode needs a lot of money up front to air on TV, and that is not something that animation studios, even Toei Animation, are comfortable or able to do. They are able to get that money through Sponsors, and the objective of sponsors is appearing at the beginning, middle, end of the episode and advertisement. So TV Rankings are highly important.
The relation you made about the most "quality" product and its importance makes no sense at all. Its sad that many people reach the same wrong conclusion.
Also for a company no section of their business is an advertisement for another, no section, except the Advertisement section itself!
This stupidity of calling less profitable areas "just advertise" to most profitable ones is highly insulting? So what happens when the less profitable area develops to be the most profitable? It suddenly turns to be the advertised one? The definition of advertisement isn't being the low denominator in profit!(In fact REAL advertisements don't even bring a profit, but just cost!)
The same ideas were(and probably still are) in the internet manga community, in this forum as well, where is believed that the magazine is an advertisement for the volume sales. And the entire reason for reaching that conclusion is the fact that volumes sell more,

. To make this opinion even wronger, the assumption is false, and in fact Magazine sell more!