This is a fun idea, but ultimately circumstantial. I don't think things are being orchestrated to the degree that you ascribe them to be. Banks are certainly interested in the space and they are certainly entering it. They may be keeping Bitcoin's price down a bit to attain more favorable pricing, but at a market cap of over $200 B, wouldn't that be pretty difficult to do for very long? It is also hard for me to believe that there are people at various banks pumping dozens of alt coins. I just can't see it.
I'm no fan of conspiracy theories, and as such, I agree with your sentiment. And am a little sceptical about OPs theory.
However, remember LIBOR? https://en.wikipedia.org/wiki/Libor#Reliability_and_scandal It was considered a really wacky tinfoil-hat-theory that competing banks would collaborate in secret, undetected, in order to manipulate the interest-rates. Yet, it proved through.
I would not be suprised to see that there is an international group of people within competing banks, attempting to get a grip on the altcoin market through a variation of schemes. Including some coördination on what alts to buy, pump and sell.