Well, in current date and time Bitcoin is considered a very volatile asset but in future when its marketcap grows to very high values then at those times it won't be so much volatile and at that time it would be one of the best or the only best asset with deflationary nature. Even at current date and time it's still a much better hedge against inflation because of its limited supply and high demand and similar due to the ones who are Hodling it for long term.
I admit Bitcoin is volatile because the price always fluctuates. However, this is the advantage of Bitcoin, it offers people with the chance of high increase. I believe Bitcoin volatility is one of the reasons why people join Bitcoin investment. If there is no high volatility in Bitcoin, people may be not interested in Bitcoin.Mate, I don't really understand that you said the price won't be very volatile when the market cap grows high. Does the high market cap really decrease the volatility of Bitcoin?
Anyway, with the limited supply, Bitcoin price can keep growing. We can check the price history, it always increases from one cycle to another cycle. According to 4 years cycle, Bitcoin is always capable to reach a new ATH. The price gap between the past ATH and the newest one is quite a lot. There is no doubt that Bitcoin deserves for a long-term holding.