Nope, Bitcoin isn't the most liquid asset out there and that is for all kinds of assets not labelled as fiat currencies, this includes stocks and mutual funds since they aren't in a liquid form. When we say liquid asset we are talking about assets that are acceptable for what it is as a mode of payment and as of right now fiat currencies are still the most accepted mode of payment out there. But you are right to say that they are not here in the long haul since companies like this one always likes to adop and open up their options just to maximize their profit.
I agree. Going by this definition, Bitcoin is not a completely liquid asset. Similar to bullion or stocks, we need to convert Bitcoin to fiat first, before it can be used for making payments. But then, we need to look at the ease of converting Bitcoin to fiat. Nowadays, the obstacles have been removed and it is relatively easy to do this. On the other hand, if you want to sell stocks, then you need a demat account, go through all sorts of KYC documentation and then select a particular stock exchange which will operate only for a specified period.