My main concern with MicroStrategy's regularly massive Bitcoin accumulation is what happens when they eventually liquidate their holdings into fiat. No matter how bullish Saylor may be, his investors will not always share the same stance. At some point, they will want to secure profits, which could lead to significant selling pressure on Bitcoin. Such a move could heavily impact the price and resemble monopolistic behavior or even market manipulation.
Your concern is very valid, it is awesome that Saylor, is relentless in accumulating Bitcoin without any immediate plans of selling. Yet we must realize that at some point there will be a plan to sell because it doesn't make any business sense to keep holding indefinitely. We can wonder what will happen if they decide to offload a massive chunk of their stash, it'll surely affect the market negatively. But I wouldn't worry myself about when they will sell because Bitcoin has built a solid reputation and it has the potentials to always reach ATH after every dip. Bitcoin can always recover when it dumps, as they're offloading and price dip it'll be opportunity for smart investors to buy the dip.