No not enough said. Not even close. Hodgdon data IS pressure tested data. With a COAL of 3.6", a 300g bullet, and H4350, the listed max charge of 81.5g produces produces 49,500 CUP. See Hodgdon pressure tested data here:
Cartridge Loads - Hodgdon Reloading Data Center - data.hodgdon.com
The max pressure spec for the 375 H&H is 54,000 CUP. No matter how you slice it, the Hodgdon data is WAAAY below any possible danger level. At a 3.6" COAL, they couldn't even get enough powder in the case to come anywhere near max pressure as shown by the compressed designation of the load. I have no doubt that you already know this.
Are you really going to assert that a pressure level that is a full 4,500 CUP BELOW spec max is dangerous?
My handloads, using the Hodgdon max charge H4350, with a COAL of 3.750 (which was .080 from the rifling) and using a 300g Hornady BTSP would have produced even LOWER pressure than the Hodgdon book loads. For a detailed explanation of why, see the following:
Berger Article on Cartridge Overall Length and Base-to-Ogive « Daily Bulletin
Your claim that .375 H&H brass is weak is also not backed up by any facts. The cartridge itself is spec'd for modern pressure with a max of 54,000 CUP or 62,000 psi. Virtually every modern magnum is based on the same case and has the same pressure spec or HIGHER. The Weatherby cartridges, based on the same case as the .375 H&H, are spec'd at 65,000 psi. Given your considerable experience, you know all of that already.
You are correct in stating that the cartridge was originally designed for optimum performance using cordite. At that time, the pressure spec was held to 47,000 psi. Original loadings from when the cartridge were introduced showed a 270g bullet @ 2650 and a 300g bullet @ 2500. Most factory loads today track closely with those numbers. Both SAAMI and CIP have since revised the max pressure spec upward considerably since then, following the post WWII availability of IMR propellants. For the most part, it does not appear that factory loadings have followed suit. No doubt you know all of this, as well.
I don't have 50 years of experience like you do. However, I do my homework on things like this before I ever start loading rounds. I follow published data and safe reloading practices. The results I have obtained from actual loading and chrono data track closely with published information, as well.
I have read many of your posts and, believe it or not, recognize and respect you as an experienced and generally level-headed fellow. It has not been my intent to personalize this, and I apologize if it appears otherwise.
Despite your experience, however, I am not prepared to believe that you know more than Bryan Litz, Hodgdon engineeers, SAAMI and CIP engineers, and Roy Weatherby combined. Likewise, I am not prepared to allow baseless and demonstrably false assertions to be passed off as fact, regardless of the experience level of the person making said assertions.
At no time has anyone on this thread suggested anything even remotely unsafe. Everything that has been discussed is in line with published and tested information. It is incorrect of you and irresponsible to claim otherwise.