The influenza virus mutates faster than SARS-CoV-2 on a per infection basis. But over the past two years we've had far more people infected with SARS-CoV-2 so the total number of mutations worldwide has been high. Over time we expect the rate of new mutations to decrease as more people gain some level of immunity and the virus approaches it's evolutionary maximum potential. We already see that the Delta variant is fairly stable and is successfully out competing all other variants in the wild.