My tank overhauls were done out of sheer annoyance. The majority of the plants I have are slow growers, but not seeing any new growth on anything for months at a time was ridiculous.
I agree that all the promises made on bags of Eco-Complete, Flourite or any other manufactured substrate is BS, but what I was doing was not working so it was time to do something else. Now my anubias are sprouting new leaves once a month. Hurray! I've also noticed that there is less melting of new plants and they recover quicker. I don't know if that has anything to do with substrate or not, but I'll take it.