So I jumped from a t5i to a 6D2, and got the 24-105 lens as part of the kit. I bought the 50mm prime when the t5i was my only camera, and I thought it was much better IQ that the 17-55mm kit lens that came with it. Everyone seems to rave about the 50mm 1.8's image quality, that it is excellent. But if I compare an image taken on the 50mm prime @ f4 with an image I take on the 24-105 @ f4 and 50mm, I think its better. Seems to have better color? I suspect they aren't even in the same league. If I end up selling the t5i, should I sell the 50mm along with it?
In the autoand semi-auto modes the camera will vary shutter speed and set the minimum shutter speed to no lower than 1/f where f is the focal length. That is the rule of thumb to minimize the possibility of motion blur due to normal unsteadiness of people.
In certain conditions, like heavy wind, on a ship, maybe medicla conditions, that is not always high enough.
Your camera allows you to set a minimum shutter speed of your choice.
The trade off of a higher shutter speed would be higher ISO settings and the associated higher digital noise.
But, noise correction is a lot easier than blur correction.
I set my camera to a minimum shutter speed of 1/200 whenever Auto ISO is selected.
"...should I sell the 50mm..."
Here's the dope. The 50mm f1.8 is a good lens it isn't a great lens. 50mm primes are difficult to use because they are so limiting. The 50 mm f1.8 gets so much praise because of its price. For what it costs and for what it provides it is a good buy. No doubt.
Now the thing is just this, it was cheap to buy it will have little value to sell used. Consider, you have 50mm included with your new, better, 24-105mm f4 zoom. The only thing it, the nifty-fifty, will offer you is a faster aperture. Is that important? Slightly more than two stops. One stop is almost meaningless to a 6D Mk II. Two or more stops begin to be a consideration.
Whoever mentioned the 50mm as a portrait isn't giving the best advice on a FF like the 6D Mk II. You will have to shorten you shooting distance which makes most people uncomfortable. A 70mm to 85mm, which your current 24-150mm zoom provides, is a better choice. Matter of fact my main most goto lens for portrait work is my 70-200mm f2.8 zoom.