Well by the same logic, one would only use their fertilizer and pay half a car for their substrate additives. It is after all what the company recommends...
It's more about understanding why and what then blindly following the company, if you value your wallet. Once we understood what was in the fertilizers we realized that a bottle actual cost was pennies.
And practice shows that many aquariums start with no problems without activated carbon and just as many have algae at the beginning with activated carbon.
Regarding traces, good looking aquariums with traces and activated carbon are out there. Does this conclusively show something, no not really.
I'll have to disagree with you there. Firstly I state right in my post, that it's not the only way to go, but the OVERWHELMING advise here is not to use carbon because it will negatively impact the plants. My point is the benefits of carbon far away any minimal if any effect it has on ferts.
Secondly of course they are selling other products. Their ferts are just branded, but most will use an equivalent of them much cheaper. It's like Seachem selling NPK or Glue vs using generic NPK or glue sold elsewhere. I'm not recommending THEIR carbon product I'm recommending carbon.
I think your missing the point with the carbon it's similar to the argument people make with water changes. They make a case that they have a successful tank without water changes. The addition of water changes gives you more latitude with light and other parameters without getting algae. Carbon to me does the same thing. The bio-filter isn't mature, carbon fills the gap. That's why it's usually removed after 6 weeks or so since by this time the plants mass has grown and the micro-organisms are there.
..And practice shows that many aquariums start with no problems without activated carbon and just as many have algae at the beginning with activated carbon.
No I don't think you can make that claim and prove it. If you took the same tank and did everything the same expect one had a boat-load of carbon in the filter at startup, I am completely convinced you would start up cleaner (Less algae). I've personally seen the difference and it makes perfect sense. There are other means as well like Purigen, etc, but I'm strictly talking about carbon vs no carbon.
BTW It should also be noted that Eheim recommends carbon at startup for PLANTED tanks.