Just how many characters is too much?

Watching several anime for some time now, I've noticed things that they all have in common: the number of characters affects how the anime would go. The more the are, the overall focus for each is reduced.

That many main characters?

Take Negima for example. On the image on the right, you would see everyone that appears at least once in the entire series. Sure there's a lot, but the focus is mostly on characters number 8, 13, 27, 28, and that kid in the middle bottom. What happened to the rest? They became just background characters, or supporting the earlier mentioned characters. I would prefer focus on no. 2, 5, 13 (again), 28 as the main characters, but guess they wasted it on filters.

In recent posts, I've mentioned about Angel Beats and Durarara having introducing unnecessary characters. That acting/vice president of the student council does seem good to introduce for a short-term character, but they kept him around for too long that, besides regaining Otonashi's memories, his presence was unnecessary and his constant arguing with Hinata was getting too annoying. In Durarara's case, the focus of all the characters featured in the opening and endings meant that, given the amount, means that the main characters (Kida, Masaomi, Anri) were given lesser importance than they should be getting. It seemed like a 3-character focus, but this somehow increased to over 20 that it has become a big mess, adding to the jumping around the timeline all over the place. Kind of reminds me of how seasons 3-5 of Pokemon seem to have this "a-Pokemon-an-episode" theme, large diversions by having filters that were not in the game they were based on, or having the main characters of the first season to mysteriously become the main characters again for any beginnings of a new region.

Rightmost top, leftmost bottom, and the 2 next to her

Who is this?

So, this brings me to the next topic: background characters. Have you seen background ("mob") characters of any anime that looks better than the main characters themselves? I mean, I could see how much better their personality is compared to the main character is. In the ending theme of "Seitokai Yakuindomo", they featured a girl from the same school the anime is set in, but is also not any of the introduced characters. Well, it's nice to have an another perspective.

In short, having just 2-3 characters and focusing on them most of the time as compared to having too many and focusing on them only once.