It is also hard for me to believe that there are people at various banks pumping dozens of alt coins.

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.