Well, FV is a special case because you can buy no drop items ; and the value is something relative as it is what you are willing to spend for. I can't answer your question for recent pet foci (after House of Thule when I stopped playing, I came back to TLPs in 2015), but as a mage the pet focus is something as the Holy Graal. I think best pet focus in current era is EM XXVI (not sure though you need to check) ; why not asking in General chat on FV or in the magician channel if a mage with EM XXVI vs a mage with EM XXIV can give you max hit, proc value and estimated hps and overall impression about pet tanking (for the same pet rank of course) ?
You could also joint the serverwide.magician channel, password is fluffy, to ask mages from other servers on live.
Sorry if I am not very helpful, but I play on Ragefire in OoW era :-) To me the jump from Vex Thal Gloves to LDoN raid augment in LDoN era (which is two steps higher) was a HUGE improvement, my pet gained 2 levels, and the improved tanking capacity was obvious. But upgrading from Ritual Summoning (the LDoN augment) to Minion of Discord (best GoD focus) in OoW era was only a slight upgrade, the pet's level stayed the same, and the max hit only raised by 1 or 2 points according to the pet type. The fire pet nuke didn't change and the water pet proc actually became weaker because of the PoP bug (someone mixed up the roman number IV and VI and the PoP water pet was casting the rank 6 water nuke, pshht).