hi twizzel, i`m a local lad to you and know very well what dark gloomy weather we get down here and i`ve got the same lens as you, i do alot of football photography for the local papers, when the weather is good i like to use F6.1 to F8 and then as it gets darker i will come down to around f4 down to 2.8 if i need to go lower which i cant then i`ll start to rasie the iso over 800/1600, and i ALWAYS shoot in aperture priority mode and find for me i have to keep the shutter speed over 1/320 to keep freezing the action.
I dont see anything wrong with your pictures at all, you like using aperture priority mode, and most people use aperture mode for sports etc etc so i would carry on using that and say to your dad keep out of it lol.