This is 100% not true. It makes a huge difference.
There is a reason why it is absolutely unthinkable to run computers without thermal paste.
I have no idea what you did wrong in your test, because when running an LED cooler it should give more output.
You probably damaged the LED by running it without thermal paste, that’s why the output was worse when you continued after 10A.
If you apply the paste correctly and your heatsink actually works, then the curve should begin dropping at much more than 10 amps.
Temperature is what makes the output decrease the more amps you feed it.
And PS the point is not to have tons more output, the point is to prevent the LED from dying, and to extend its lifespan rather than having it degrade 2x faster than necessary.
Those are results from real tests.
You can look up any thermal paste benchmarks and you will see how horrible no paste is.
I can’t believe that this isn’t common knowledge in the flashlight world, it’s just ridiculous. In any other electronic or mechanical field everyone knows how important thermal paste is.
You should redo your test properly, using an LED which hasn’t been driven to 10 amps without thermal paste, and use an IR thermometer to monitor the die temperature.
Without thermal paste you will probably see 100 or 150C+ which is why your domes are burning. With proper cooling this will not happen.
Even a small flashlight-sized heatsink with thermal paste will perform better than a 135W heatsink with no paste.