If form factor is a main concern I am wondering why no one is suggesting the EOS M5 or M6. The adapter for EF lenses does not effect the AF or tracking capabilities. Also due to mirrorless there would be no front/back focus issues.
The SL2 rebel has no micro adjust function so this is a deal breaker for me. I see not real negatives going EOS M6 as it also functions like a mini 80D but with an electronic image stabilizer.