The first .458 and .375 I ever fired were the personal rifles and hunting handloads of a respected gunsmith. He was rather large - had an 18" neck! - and had filled the stocks with lead. They balanced and shouldered very well, slowly, but well, and he cautioned me to just let the recoil push me back, and not to fight it. The .458 was loaded with 510 gr. Barnes bullets.
I was amazed at the deep sound, and remarkably softer and slower push of the .458 over the somewhat nastier .375 H&H. Shooting from a bench seems to potentiate felt recoil greatly. One of the most unpleasant firearms I have ever fired was an 18" barreled Winchester 3" 12 ga., off the bench. Bench shooting removes all of the body's recoil absorbing flexibility, and such repeated shots are rare in the hunting fields. It also seems to focus one on the rifle, not so much on delivering a devastating effect upon the "target."
I have since realized that longer barrels are much better choices in all firearms, regardless of cartridge, for power, accuracy and follow-through, and lessened muzzle jump (the most objectional part of recoil), and lessened muzzle flash. The difference can be startling.
Heavier and longer rifles and handguns just work a lot better. Easy carrying is great, but if one's main interest is in hitting the target well, and delivering a telling blow, or several, weight and length is your friend.
I grew up thinking that shorter barrels were a great advantage, and in dry fire, seemed to come up faster, which I took as the key to hitting game, or defending myself. Later on, through using firearms in many different circumstances, it became clear to me that just having the sights pointing at the target was in no way a guarantee of hitting it, or accomplishing the task well, should I hit it. Powder burning/pressure developing barrel length, follow through, stable pointing/aiming, muzzle jump and flash....all adds up to success or failure. Failure can be disappointing, ugly, or dangerous, so facing the truth of what REALLY works is important. Now, I would rather carry more gun, than miss or wound. I would rather have less magazine capacity and a longer gun.
I wonder if one sat lower, making more of a standing type geometry, your .300 would be more pleasant to fire?
Bench shooters can more or less ignore the gun weight. I only carry these a few yards from the truck to the bench and back again.
My .300 Win Mag bench rifle weights about 20 pounds with scope. I had my dear friend and rifle builder extraordinaire, Lee Six, put extra weight in the stock. Even so, an afternoon at the range with the .300 and about 80 rounds does take its toll for the reasons you state. All the recoil is transmitted to only the upper body; the lower torso and legs do nothing to absorb any of it.
Shooting the large caliber pistols is another matter. I have taken to downloading the .454 Casull and the .475 Linebaugh to mostly .44 mag recoil levels. Occasionally I get reckless and shoot full house loads, but never more than a half dozen at a time. In the hunting field, these would be great because only a shot or two would suffice. Target shooting with the Linebaugh at top end loads gets tiresome (for me) rather fast. After a dozen or so accuracy suffers. I use heavy gloves (like John Taffin) to soften the recoil and save my hands from tendinitis and the possibility of early arthritis.
Oops.
Make that a 19 1/2 inch neck. I remember now, because we tried to see if he could be strangled by a normal human being one night...just to do something practical with our purely medicinal beer investment, while nursing our shoulder bruises.