Excel is pretty powerful stuff and if you have other primitive plants in your tank like mosses, Vallisneria and ferns, they might be damaged.
More plants is a good way to control algae. Aquatic plants are a more complex organism and use the added nutrients in the water more efficiently than algae. I used Brazilian waterweed (Anacharis) in my tanks when I had a problem with "hair" algae. This plant thrives in water with higher levels of nitrogen and potassium, the same as algae.
I also got some "Ramshorn" snails. These little guys are second to none in eating all forms of algae. These natural methods may take longer to do the job, but by using them, you don't have to worry about reactions to harsh chemicals.
Just a suggestion, you're the tank keeper.
I do think you're at least partially correct. I did a big trim of my stem plants because they were growing crooked, and the stag horn popped up after that. I think I removed too much plant mass. Luckily, the Excel is helping the stems grow back fast.