The wire nuts are not a source of heat if tightened well, they are just exposed to the ambient themperature. This only proves that the luminaires have crap thermal design. Or UV exposure is what happened

Maybe they were designed with 50..70W lamp in mind, then somebody in RAB figured that the 175W lamp + gear still fit in by size, so they decided to assemble them in 175W too

My place of work had 16 low bay MH of 400 watts each, mounted at about 30 feet (9 m). They were all remote ballasted, with a wall of ballasts in a ventilation/electrical room. They were installed in 1988 and all of them worked in 2012 when they were replaced with T8. I can see however that wall packs would have a higher ballast failure rate as the heat is higher.

The thermal conditions for remote ballast are by far better than for ne tightly packed with the lamp in a plastic enclosure. And the old ballast may have been of higher quality to begin with

I'll snap a few photos of the wall packs the next time I am down at that building.  I have 2 of em in storage that I am going to turn into 150 Watt HPS to install at other buildings.  They are nice looking packs, but definitely not for anything over 150 watts.  Essentially they look like what is at this link, the black colored one.

https://www.reynoldsonline.com/ASSETS/DOCUMENTS/ITEMS/EN/RABEWP2H100QT_Broc.pdf

I'll snap a few photos of the wall packs the next time I am down at that building.  I have 2 of em in storage that I am going to turn into 150 Watt HPS to install at other buildings.  They are nice looking packs, but definitely not for anything over 150 watts.  Essentially they look like what is at this link, the black colored one.

https://www.reynoldsonline.com/ASSETS/DOCUMENTS/ITEMS/EN/RABEWP2H100QT_Broc.pdf

Can you sell the old ballasts on ebay?

Its sorta weird, it does not look like 175W vs 150W would make all that great difference with temperature. Yet we have identical wallpacks here in 150W HPS and they are working trouble free for 20..30 years and counting