Can’t add much arms and/or bombs to that frame design, and a low and slow plane is a great target for anti-aircraft arms.
I always thought the A10 Warthog was the best of the air support frames because it is extremely tough and provides the pilot with a lot of protection—not to mention the massive main arsenal it carries:
Armament: One 30 mm GAU-8/A seven-barrel Gatling gun; up to 16,000 pounds (7,200 kilograms) of mixed ordnance on eight under-wing and three under-fuselage pylon stations, including 500 pound (225 kilograms) Mk-82 and 2,000 pounds (900 kilograms) Mk-84 series low/high drag bombs, incendiary cluster bombs, combined effects munitions, mine dispensing munitions, AGM-65 Maverick missiles and laser-guided/electro-optically guided bombs; infrared countermeasure flares; electronic countermeasure chaff; jammer pods; 2.75-inch (6.99 centimeters) rockets; illumination flares and AIM-9 Sidewinder missiles.
The Pentagon has tried to kill it off time and again, but when air support is the mission they keep bringing it back.
But if you want old and (relatively )slower than jets and time on target, why not the P51 Mustang?
The water cooled engine was fragile and highly susceptible to damage from ground fire. The radial engine on the P47 and A1D were far more durable. But alas, we now live in the turbine age. I do from time to time hear rumors of folks trying to develop Diesel engines for aviation ...
Not a good ground attack plane. It was liquid-cooled, and many a pilot was lost when the engine seized from the damage loss of coolant and the pilot had no altitude to [successfully] egress.
Years and years back there was a great article by a Marine (O6 I think) in USNI Proceedings making the case that the ideal escort for the V-22 Osprey was an F7F Tigercat upgraded with modern avionics/weapons and turboprops.