Why? I'm certainly no expert but I've read loads and haven't really found advice not to use MG ubiquitous. I'm attracted by their claim of 3 months worth of nutrients which seems just about perfect for an auto. Do plants consume every nutrient available in the soil or do they just suck up what they need. I know that if us humans have a deficiency in a trace element, we often develop a craving for a food that contains that mineral.
http://www.lovethegarden.com/product-details/miracle-gro-all-purpose-enriched-compost-20litre
If you have the time and wouldn't mind, please explain to me why you think it's not a viable growing medium. IMHO, growing dope isn't rocket science or brain surgery (although it seems many would have you believe otherwise) and I suspect a lot of people's problems with growing are exacerbated by using too many nutes or just by fussing too much!
I use tap water and whatever compost I can buy mixed with however much perlite I can afford because I know it works. It's similar to my approach to cooking chilli . I don't weigh my ingredients and I may use different ingredients each time I cook the dish. I add them ad-hoc and taste as I go along. I may not get a completely consistent recipe, but my chillis are usually amazing because they are created with love and passion.
Be kind to your plants but be aware that sometimes too much kindness can kill. Lol - yeah that sounds like a thing!
I just water my plant and the only bloom supplement I'm using is water that has been used to steep banana skins. I'm interested in your reasoning. My Himalaya Blue Diesel has thrived in MIracle-Gro - I admit I do have a slight gnat problem, but that might have started with the previous grow which didn't use MG, but B&Q. (A UK DIY store in case you didn't know.)
Peas and Love man