Alternative to Canon 28-300L
You have a dslr, you can change lenses, this is a very usefull feature that you should be using.
Look at the focal lengths most used and sample some primes. I would suggest the 24mm L II for example would give significantly better IQ and give you f1.4 as well.
Add the 50mm f1.4m, 100mm L IS macro and the 300mm f/4.0 L IS and you would cover the range, get far superior IQ, be easier to hold the camera, and have 4 stops more light.