I feel like I have the main piece of the puzzle when it comes to creating a profitable business....products that people want
You have it backwards.
Sales is the main piece of the puzzle. Not product.
I can go to one tradeshow overseas and find 100 products worth selling in three days. Product is important, but not as important as sales.
If I was you, I'd work on learning marketing/selling, but I'd do it by concentrating on a niche outside of t-shirts, where the margins are higher and the competition is smaller.