You don't need substrate fertilizing when you use the EI method for fertilizing. Aquatic plants can do fine with just water column feeding. Having a fertile substrate is an advantage in that it provides an alternate or back up source of nutrients for the plants. If you take a few days off, for example, the plants will still have nutrients from the substrate. Your ADA substrate is good for that.
If the sediment is also rich in terms of ferts, like the ADA AS etc.......then you get a longer life out of the ADA AS, and you get more out of the water column dosign as well.
It's not a question of either or, rather, both working together to provide non limiting conditions.