An interesting and wide ranging discussion, so I'll share my 2¢ worth. I've been a fan of the Hi Power since the '60s, and have owned I don't know how many. They are a great pistol IMHO, but I would not describe them as particularly "heavy duty". In Olden Days, I shot all manner of ammo in some of mine, including hand loads that would probably be considered +P or +P+ now. I suffered no catastrophic failures, but admit I'm more circumspect now days about what ammo I use in Hi Powers. The slides and frames are a bit on the thin side, but the potential Achilles Heal I think about most is the barrel cam in the frame. I've seen the ugly photos of broken cams, and reports of the difficulty and expense of replacing them.
I have a 9mm 1911 or two. I'm not at all offended by the extra steel in these as compared to many other 9mm pistols. Kinda like all that extra steel in N-Frame S&Ws chambered in .38 Spcl. or .357. All that extra steel in the 1911 equates to soft recoil, even with the most energetic 9mm ammunition, and no concerns at all about durability. I've found the modern 9mm 1911s with the integrally ramped barrels, and using the excellent 9mm magazines available now days, has resulted in my 9mm 1911s being as reliable as 1911s chambered in the "proper" .45 ACP or 38 Super cartridges. Life is good..