Do my angelfish need an airstone when I have a hang-on the back filter with a strong current?

I turned off the bubbler and they seem to be swimming more freely.

The bubbler probably isn’t making much of the current they are experiencing.
And if there is much of a drop at all from the filter to the tank that’s probably aerating the water plenty. ...You could remove the bubbler without much affect.

If the fish want less current consider putting a set of plants or decorative baffle between the filter output and where they like to hang out, creating a less turbulent area.

I have both an outside filter(Aqueon 55) and an airstone, but my tank is bigger, 46 gallons. I do notice that the angelfish tend to stay out of the area where the water is coming in from the filter. The main reason for the airstone is to stir the water to help it absorb oxygen; if you’ve got a strong current from your filter you probably don’t need both.

Don’t turn off the bubbles, they enjoy it. you should try putting a strong current in the tank if you have angelfish, but not for the cories. Put a medium current in the tank if you want to make both of them happy.