Alt coins are definitely easier manipulated. I've been watching the sell walls develop on vertcoin for weeks, while the price has stagnated and the coin has gone from top 30 to top 90, and one whale has accumulated over $15m worth in the matter of weeks.

The only part of your logic that I don't understand, is how does pumping alts lead to them accumulating more bitcoin?

The other side to what you don't mention is that the institutions are backing ripple because it is not decentralised, so with a bit of influence over the company they can have more control over the coin than they can with Bitcoin