The way I view it is that, in these unnatural environments that we create for our fauna and flora, we have to provide fuel for the health and growth of each. In the case of plants, we either do it in the substrate (which also leaches into the water column) or directly into the water column.
The various active substrates provide a package of nutrients that is consumed over time and then the entire substrate needs to be changed, which can be done in phases. The various AIO fertilizer packages do the same thing, but are much smaller packages requiring more frequent administration. Both approaches attempt to simplify success and are particularly good in low-medium light setups. However, high light setups usually require much more active participation on our part to establish a balance that works in our individual tanks.
There are many of us that use inert substrate only and have no algae and excellent plant health. It allows us continuous nutrient consistency and control via column dosing and the substrate almost never needs to be changed. However, active substrate is as close as we can get to a set-and-forget approach …but, as you know, it still needs to be watched for the gradual fuel loss.
You don’t need to follow EI. It is an attempt to get closer to a dosed set-and-forget approach, but isn’t the only method. There is the PPS approach, which is a minimal nutrient and w/c regimen. Many of us settle somewhere in between.
You can add the plant-preferred nitrogen via urea (many threads on this on TPT). I currently add only urea for nitrogen (fish food, of course, is another source) and do a 50% w/c bi-weekly. Many of us believe, strongly, that water changes provide far more benefit than just nutrient resetting. There are high CEC substrates that can absorb and release some nutrients but, again, you still have the control issue where you don’t know how much is actually being released. In a high light tank, it is a matter of finding the right balance of light, CO2 and fertilizers for your particular tank no matter what the substrate approach.