@Tazzieman I don't think your statement on FrontRunner is correct, FrontRunner refer you to the vehicle manufacturer for their load ratings rather than making a claim. See my Q&A with them below.
It appears they focus on engineering their platform to exceed the vehicles rating so it's not the weak point. I enclosed Front Runner's response.
After all it's the Grenadier's gutters you are attaching to.
And the Rhino rack calculations and figures are not available for the Ineos through Rhino, so you only have the roof rating figures from Ineos.
I contacted Front Runner and asked before buying the Slimline II and got the answer below:
View attachment 7822173
NOTE: I have the 3/4 Slimline II rack as I have Safari roof and an Ineos released Rhino rack is not available yet (While it's coming for dual cab ute but I couldn't wait).
For the 3/4 Slimline II rack they supply 4 legs each side but the legs are slightly less wide than the rhino legs where there are only 4 for the full size rack.
If you were worried you could fit six legs in going with spacing every 2 slats, and get the same metal cross section in the channel.
I have fitted the Slimline 2 and the gutter mountings are superbly engineered. I am very impressed. And for those interested it weighs approx 43kg.
Regds Doug.