Okay, so not obsolete. I wonder how many .450 Marlin rounds are out there taking game from deer to elephant in a given year, what percentage this would be of the number of .375 H&H rounds taking the same game each and every year to this day? Let's just narrow it down to cape buffalo, what would be your guess as to the number of cape buffalo taken by the non-obsolete .450 Marlin in an average year? Zero? One occasionally? Ever? How about the H&H? Who wants to lay odds that a buffalo dropped to a .375 H&H on this very day?
Let's cut to the chase as good hunters do. From Oxford Dictionary - "Obsolete, def: no longer produced or used; out of date."
So is the claim that the .375 H&H is obsolete literally true or literally nonsense?
"Obsolete, def: no longer produced or used; out of date
There you go, answered it yourself. Out of date.
When was the last time a cartridge was designed that looks like the H&H? About 100 years ago.