With your example, you're saying that a significant amount of algae can co-exist in a healthy planted aquarium (since there's no competion)?
Yes and we do see that also.
Generally the Green algae do well, BBa can, Diatoms do, BGA as well, but at very low levels.
Algae spores as well as adults respond to nutrients change/environmental cues in aquatic systems much more than plants..........
Adding some NH4 vs NO3 makes little difference to plants, adding NO3 vs NH4 to algae really makes a large difference, especially when adding high light.
Influx of high NH4 means it's a good time to grow and bloom with a high chance that the alga will be able to complete it's life cycle till the "next season". For some folks, it's always next season because they do not address a stable place for the plants to grow well and consistent.
CO2 is preferred by both plants and algae but it can really help plants much more. The plants take about a week to adapt over to high CO2 or low CO2.
Neither plants nor algae are competing form CO2 when we add that...........
But do we hear hobbyists running around telling everyone that the plants are outcompeting the algae for CO2?
No, so why would it matter for the other nutrients?
It doesn't.
Going from high CO2 to low CO2 is very detrimental to plants, whereas algae are not DIC limited, plants are. Algae respond in a few hours or less to flux in CO2 levels. Algae have enzyme uptake kinetics that are far more favorable to a low range of water column parameters than plants.
Best plant growth is where there are stable water levels, rich nutrients, good CO2 and clear water.
If no new flux of NH4 or CO2 variation is present, the adult algae decline and slowly die off, adding some pruning, herbivores, manual removal, cleaning, adding more plants etc beats the adult algae down even further.
A management method I often refer to is using "many little hammers to beat the algae or weed down". Most aquarist want to use one big hammer.
I view algae in our tanks as weeds. The plants we keep are weeds in many cases.
So aquatic weed science is not a bad field to be in for control and management for lakes, streams, impacted systems etc.