In the United States, regulations used to prohibit TV networks from producing the programs they broadcast, except for news. The networks needed to contract with studios that were owned separately.
Deregulation beginning in 1990s now allows the networks to produce their own programs. As you say, this allows concentration of control over the network programming, but I think it is counter-balanced by the vast amount of content that is now available for the Internet. In spite of more concentration of the giant media corporations, it is easier to find diverse content online than ever before.
I have to say TV series in the US since the deregulation are diverse and of very good quality. But, there is still a very high concentration as a few companies own almost everything, specially since Disney bought Marvel in 2009 and Lucasfilm in 2012.
The only very annoying thing is that the networks tend to cancel their own best shows for reasons I cannot understand. You know, great series with very high ratings like Firefly (Fox network) and so many others.
Actually, Firefly had low ratings, but it was not as a result of quality of the production.
FOX scheduled it on Friday evening, a time slot in which science fiction has never succeeded on FOX. They broadcast episodes out of order. They frequently preempted the series for other special programs. It is not surprising that the series did not develop a strong following, even though it was very well done and has since become a cult classic.
The executives who make programming decisions are NOT creative people. Their management training does not encompass creativity, only dollar and audience numbers.
Yes, it a miracle people loved the show so much, because the broadcasting was so messy. Nevertheless, 9.1 on IMDB :)
Firefly won a Primetime Emmy Award in 2003 for Outstanding Special Visual Effects for a Series. TV Guide ranked the series at No. 5 on their 2013 list of 60 shows that were "Cancelled Too Soon".