What do 'dumbed down' and 'high brow' mean here?

[Maggie]

Hi,guys

There is one paragraph below that I don't make sense. Please help me if possible.

[Diverhank]

1. I think the author simply wanted to convey the idea that the quality of programs has gone downhill -- getting dumber over the years...there is no specific number of years here.

2. The author meant TV broadcasting programs from the "high brow" channels, not TV versus some other forms of broadcasting.
3. The term "lion's share" means a majority. The term comes from a fairy tale where a lion and 3 other animals hunted a deer but he took most if not all of the meat because he's a lion, king of the jungle.