I wouldn't say that it means almost nothing, but it means a lot less than most users think. I know what terps and minor cannabinoids I like and how they affect me, but I also know that flower under ~20% THC will leave me too lucid to reliably get to sleep, which is my primary medical use. But you definitely can't go off that number alone like so many customers. It's not a perfect analogy, but I think of it kind of as the THC percentage being the base magic power of the flower/character, while the terps and minors are the spells and elements and shit that you actually use. That measure is both essential to the effects of the flower and next to useless by itself, like the magic stat on a character with no spells. A flower with high THC and low terps is like a character with high magic power fueling low level spells.

What is absolutely correct is that the worst, laziest consumers don't know about any other number and refuse to listen or learn. People who know that they matter, who enjoy them all and tell me to pick them something good, I respect. People who tell me "CBD doesn't do anything for me!" and insist on the flower with the one big number when I suggest a CBN edible to help with their insomnia I do not respect. "I need the highest for the lowest" is worse than "I only smoke an unstable dihybrid cross from the 70s" but they frequently go hand in hand.