I personally consider Stanzz as an extremist/purist. I have disagreed with him a number of times on this forum with regards to others husbandry practices, because not everything is black and white in this hobby.
Having said that, in this instance, I happen to agree with him 100%. Jags are not suited for 75 gallon tanks, and anyone that has kept one long term knows this. Jags are open water predators, so even if they did stay the size of more of a cave dwelling species such as a midas, the comparison still doesn't equate due to the behavioral differences between the species. Some fish sit idle for much of the day, other more open water predatory species are on high alert cruise mode 24/7. Choose a different species, or upgrade in tank size, are the two most sensible options available to you. Good luck.