Second take on Tamron 16-300mm on my Canon EOS T6i

[4rum]

I had mounted one earlier on a Nikon, D7500 and was/am extremely pleased with image quality. I was not nearly as pleased with image quality when I mounted on on my Canon T6i. It did lead me to get the Canon 55-250 STM, however. I'm VERY happy with the image quality I get with that set up. Now, I know there is a huge difference in processors between the D7500 and the Canon, but I didn't give up on the Tamron 16-300 lens. Picked a day with good light, wanting to give the lens every chance to perform. I started upping the ISO. Oh, shooting aperture priority, manual ISO. Image quality improved to at least 'satisfactory'. Seriously, image quality did improve noticeably. I'm continuing to shoot with the Canon EOS T6i, mostly wildlife and nature, hand held. I had given a D7100 to a friend. It is more than she wants to learn and is sending it back. I am anxious, now, to put the Tamron 18-400mm back on it and try those same settings, adjusting the ISO just to see if I get similar results.
Well, I think I've about whipped this dead horse, but would like input, suggestions, or similar experiences. (I do have a tripod, in the field it is unwieldy.)