Yes, I think that is possible. Individuals can directly influence the value of bitcoin if they buy bitcoin in bulk. The value of bitcoin can increase. We know that the amount of bitcoin is limited. If it is big investment. It will directly affect the value of bitcoin and create price fluctuations
I agree if Bitcoin wants to be taken seriously it probably shouldnt be this easy or legal to manipulate the markets. While decentralization is supposed to replace regulation its clear that there is still a way to go before it can be truly taken seriously. As mainstream finance invests in cryptocurrency assets and as countries take steps toward legalizing bitcoin as a payment system method like to other country instead,