The crucial question remains: Who should buy MSTR shares if 1) one can buy Bitcoin directly and 2) one can buy ETFs if you want a leveraged exposure or don't have access to BTC spot, if both of these options are cheaper than MSTR regarding the risk premium? 21 Capital should have the same problem. The only really important reason I can see is indeed volatility just due to the risk premium, but you could simply increase your leverage on ETFs.
If you buy MSTR, beside the leveraged BTC product, you are buying the biggest BTC holder with a corporate infraestructure and free cash flows from being index funds bought all over the world. They have the possibility of becoming the world's biggest Bitcoin bank in the future. It's the nationality of what being the #1 holder gives the company to do things. The best investments are usually monopolies. And MSTR is a monopoly because they simply were there first and took the risk, they are not shady monopolies like Google or Facebook which constantly try to screw up competition. Saylor is doing the opposite, he is teaching competition how to replicate their model if they want. It's all open sourced.