Random results do not equal scientific testing. Someone would need to use the same herb process both ways and then get both tested. Random tests of rosin do not show that it is more potent then bho.
Your right, it is not hard evidence, however one starts to notice patterns after a while. It takes a skilled cls operator, and most likely super dank material and dewaxing, whether with an accessory solvent or inline with di, to produce bho with numbers above 80% thca/9. Terpene's are a whole other matter that not only has to do with the operators techniques and equipment, but also has a lot to do with the vac purge which anyone who has done it a lot will openly admit it's a dynamic art form that even after years of practice, they still have not mastered. Most bho analytical reports I've seen from people that arnt experts, are very poor to the ones I've seen from people's rosin, who also are not experts, as I believe at this moment there are no rosin experts. The over all simplicity of rosin allows for less variables one needs to control. You are correct though, and I had previously stated as well, there is not that much hard science with rosin yet.
You forgot the starting material needs to be tested too, in order to show a control factor for comparison of numbers if one would like to produce percentages of loss or concentration in any of the volatiles.