So do the whales have the ability to dump us into a bear market on their own?
For bitcoin it won't work because a bitcoin whale is part of a much bigger market that has its own directions and won't change those directions if a whale dumps. For example last year there were many whales with a lot of bitcoin who were trying to dump bitcoin to crash the price below $3k but they couldn't and they lost a lot of money trying to do so.
In altcoins things are very different because they don't have bull/bear markets instead they have pump/dump periods and also an altcoin whale usually controls the whole altcoin's price and its direction. If the whale wants to pump it they can and if the whale wants to dump it to move to next shitcoin to pump they can too. That is what they do almost every day to maximize their profit too.
They would be able to buy cheap Bitcoin but if we're in a bear market they can't sell for huge profits (and then rinse and repeat) until the next bull run. Or is Bitcoin accumulation the be all end all for them?
Everyone can buy cheap bitcoin when price has dropped unreasonable like these days. It is not a whale specific thing. And that is what the day traders of all pocket sizes have been doing from day one that bitcoin was worth below $0.01 and was listed on the first exchange.