Comparing JVC to DSLR

I have had a little experience both with the JVC and different DSLRs, however in the most recent experience both cameras have been problematic. when using the JVC, we had problems with focus and white balancing, we zoomed in focused the sense but when zoomed back out in the desired shot size it would automatically be unfocused again. we then realised we had to play around with the focal length and that sorted out that problem. later when discussing the problems we had with roddy he showed us that the camera was switched onto automatic. this taught me that every time I take out a piece of equipment to check the settings thoroughly and don't assume they'll be correct. I took out the 6D for my photo portfolio and my theme was London at night, I then realised no matter how much I rack up the ISO my images would still be very under exposed. I managed to take a couple nice shots but majority were unusable. This taught me that I really need to reccee the location before taking out the camera and therefore I had to use a 1300D which meant my pictures were not as crisp as they would have been if I used the 6D. Overall my experiences with both cameras were not the best, I need to keep practising and making sure I check beforehand both the settings and locations.