I disagree. I had a look at
my AX Krait; it has three HRPs, all G5 heavy duty / deep plating. Two are class 5, one is class 3, and it has a total armor of 3,061. The small slots are occupied with MRPs and an AFMU.
If I replace the 3D HRP with a guardian, my raw armor drops to 2,895, and with the caustic resistance factored in it is 3,048. Hardly a difference, but the idle heat EDSY shows is raised from 12.7% to 13.1%. The next HRP I could replace would be a 5D, replacing that one drops my raw armor to 2,647 and 2,933 with caustic resistance factored in, while raising the idle heat to 13.7%. Also the C5 GMRP would push my power use to 103%.
My other AX build is a
Chieftain, which has pretty much the same build philosophy. It has three 4D G5 HRPs in the military slots with a total raw armor of 3,268 and the small slots are, again, filled with MRPs and the AFMU. Replacing one of the HRPs with a guardian one drops the armor to 3,057 raw / 3,218 caustic, replacing two to 2,846 raw / 3,153 caustic. Two guardian HRPs also pushes it to 103% power.
Power is a problem if you run a low emissions plant (as I do on my Krait) or have a ship that is otherwise on edge for power.
I would say generally GHRPs are not worth it for builds where the smaller classes (3 and below) are used for stuff like MRPs or AFMUs, which is how AXI recommends it. Again, GHRPs are a good alternative if you don't have the engineer unlocks or materials to go beyond G3 on the HRPs.