understand something... first your teeth are bones and should be a "bone white" NOT a bleached or chemical white so do NOT compare the color of your teeth to THE "falsely" promoted ideas about what white teeth should look like!
Everyone knows someone who has had their teeth "whitened". In each case it looks almost grotesquely unnatural to me.
Second - baking soda should not be too bad to use... it has many benefits. I can tell you that my mom brushed her teeth with baking soda till well after she got married and still has her teeth at 73...
third - does your "natural" toothpaste contain glycerin? This is where the "shine" is coming from and it coats and prevents your teeth/bones from conducting normal metabolism and re-mineralizing.
The baking soda most likely just removed the "unnatural" shine/coating of glycerin from your teeth IF, there is glycerin, or a similar active "agent" in your toothpaste.