FaceTime and Zoom video quality issues on MacBook Pro

It would be good to check two points in this scenario.

A. The connection from your MacBook to the Wifi access point

B. The connection from your Wifi access point to the Internet.

You've already confirmed you have 300+ Mbps to the Internet, which is great. If you indeed have this bandwidth available, then the issue lies in A., your Wifi access point. Here are a couple of things you can do:

1. Connect with your MacBook to your Wifi access point.
2. In the top right corner (menu bar) you should see the Wifi icon (that looks like an umbrella-ish)
3. While holding down the "Option" key on your keyboard, click on the Wifi icon in the top right corner of your screen.
4. 
5. Under TX Rate, you should have something higher than 30, ideally 100+ Mbps. If this number is smaller and/or changing in front of you eyes as you look at it, it might be a sign of an unstable Wifi connection.

Next, let's check your internet connection. Run a speed test to find out how much bandwidth you'll have from your MacBook to the Internet. This should be something smaller or equal to the 300Mbps you've mentioned before.

I always use the Speedtest.net under this URL: https://www.speedtest.net/

Run this and check what the speed is. It should be close to your 300Mbps. If it's not, then your Wifi access point is limiting the bandwidth you'll get on your MacBook, which results into choppy FaceTime quality.

Also, the use of VPNs could impact this as well, so be aware of that and possibly switch off any VPNs you might have running.

Hope this helps!