bitcoin is not spread evenly yet, so it is still possible to control the market. anyone who have capital can control the bitcoin market. but bitcoin also depend on the sentiment, good or bad sentiment can influence bitcoin price. sentiment factor only give small effect, capital give biggest influence in bitcoin price.
It's not easy and look at how big the bitcoin marketcap is, they have to have a large amount of money and find a place that sells that much bitcoin, if an exchange has half the number of bitcoins in circulation it's possible, but bitcoin is spread across many exchanges that make it difficult for a group to move the bitcoin price even if he has a lot of money, and again their competition is many, whales are not just one or two, and these institutions are competing with each other.
And who has that much money? Even microstrategy, which is now famous for holding lots of bitcoins, when they sell their bitcoins, I'm sure bitcoin will still return to its proper position in the future.
Speculation from people who have popularity and or big world governments that have influence in the world economy will definitely give sentiment that affects the bitcoin market, we have seen that a long time ago, saying bitcoin scam, ponzi and so on, but they are silent when bitcoin reaches The ATH is annually, this is possible, but it doesn't have an effect over a long time.