I think that's changed quit a bit over the last few years wiith things like weeble and robinhood. but I'll look into it
Places like robinhood take all crypto purchases/sales and feed it into an algorithm to garner profit for themselves. In a lot of cases when people buy or sell on there robinhood don't actually do anything. They just wait for users to cash out at a loss. So deposit $500, trade for a month, cash out $400. Robin hood don't do anything with your trades, they just keep that $100 you lost for themselves. Remember the are far more losers than winners on those trading apps
Also when there are big price movements and increased selling and buying like with doge SNL and the bitcoin dump yesterday, they'll conveniently go down. Those type of events leave their system open to heavy loses.
USDT is another shill. I have already posted how they are trying to avoid an audit. They don't hold the reserves to back the sums they hold.
Binanace doesn't hold billions in USD, it holds bitcoins which is tied to the USD. Alts on exchanges are therefore tied to bitcoin and not USD. Everything else is either an illusion or a house of cards.
Your point about bots does hold some truth though. They aren't however manipulating alt coin prices, it's just arbitrage.