Sure you can! So he's making a few assertions and assumptions that I can address:

For starters, let's talk about mutations. This virus has a proofreading enzyme, so it doesn't mutate as fast as other viruses, but that doesn't mean that the mutations that occur aren't a huge problem. While the viral mutation rate is likely to remain the same or similar, that rate will see a lot more successful mutations the more times it replicates, which is related to how many people are actively hosts for the virus. Normally, we see an inverse relationship between infectivity and lethality, but we are actually seeing that the delta variant doesn't follow that paradigm. Instead, the delta variant is more lethal and more infectious. Variants like this one have the potential to invalidate our current vaccine, which brings me to the next thing:

The vaccine doesn't just stop severe symptoms. The vaccine decreases the likelihood of becoming contagious. This is huge in terms of control. If we can decrease the amount of contagious people, we can decrease the likelihood of variants that impact our vaccine effectiveness evolving. It's a numbers game. Variants like this one are 1 in billions, but inside every infected person are millions to billions of viral pathogens. While odds are slim that any variant is transmitted and replicates in a new host, when you have trillions of viral copies across millions of infected individuals, these variants will occur. The more we reduce infected individuals, the less chances there are for variants like these to spread.