the internet is interconnected...yes..
..but ISP's are not centralised under one company, which are all using one DNS
its funny how you start your idea by literally using a plural to describe ISP's and not a singular context.
just because computers are networked together does not make them a single entity controlled by a single point of failure/entity.
the internet has different ISP's in different countries with different policies. if it was all centralised, wouldnt you think russia would have taken out the US 'subsidiary' of your imaginary conglomerate by now
With your argument banks are not centralised either, because there are many banks all over the world.
I know ISP's are not one entity. But they are all centralised in the way that each of them facilitate access for more than one singular user each. I believe that all countries have a cooperation between ISP's and goveernments, which have the potentiality of ISP's being used as tools by tyrannical leaders to silence opposition. That is the type of centralisation that is definitely not beneficial for humanity.