Yeah, henna is definitely not for everyone
At the same time, I notice a lot of people go crazy adding a ton of protein content to their henna: protein-rich conditioner, oils high in protein, yogurt, eggs, mayonnaise ... stuff that when combined with henna can create a total nightmare because henna already coats the hair, acting as a protein, and adding actual protein over it is ... ugh. Drying as all get out.
I wrecked my hair a couple months ago by adding loads of pectin, AKA pure protein, to my mix to thicken it because I made it too runny. My mix already contained conditioner w/protein (for a semi-gloss treatment). Guilty as charged. Plus, when the color came out too dull, I turned around the next day and mindlessly re-applied the last of the batch. Just horrible hair for 1.5 months.
Most of us can probably agree that henna has a steeper learning curve than commercial hair dye. But I understand you're saying you are just one of those people for whom henna in and of itself is not your soul mate. I feel the same way about glycerin