What separates them is not spendability but what a payment exposes. Monero hides sender, receiver and amount by default, while bitcoin leaves every transfer visible forever. That cuts both ways with merchants: some refuse traceable coins, others refuse untraceable ones because they cannot show where the money came from. The gate that decides real-world spending is the fiat conversion at the end, and both chains pass through it.

Two structural differences matter for the longer run. Bitcoin has a second layer with its own liquidity, so a payment can settle in a second without waiting for a block. Monero has no comparable overlay and its payments land in minutes. The other is the security budget: Monero pays a fixed tail emission to miners forever, while bitcoin has to replace a shrinking subsidy with fees, and nobody knows yet whether that fee market will be big enough.