I continue to hold the 88mm as an exemplary model for a multi purpose weapon.
Even the 8.8cm Flak (anti-aircraft gun in several versions) had limitations. In the air defence role it needed a "fire control computer", radar, and or range finder/predictor to properly orient on aircraft targets. In the ground role it was as high as a barn needed careful positioning to be effective and protected. Early on that protection came from its superior range but that faded with time. The 8.8cm Flak led to the development of the highly efficient high velocity ammunition to be used in several versions of armoured vehicles like the Tiger, Tiger 2, Nashorn, Jagdpanther, and the 8.8cm Pak 43 (anti-tank gun). None of these could be used in the air defence role.
The 8.8cm Flak wasn't the only gun that early on had dual roles. The American 90mm and the Brit 3.7 inch (94mm) QF AA gun all had the same characteristics - a high velocity flat trajectory round that could outshoot the early anti-tank guns (40mm 2 pdr, 37mm US) and 57mm 6 pdr). The 90mm found a place in the M36 tank destroyer and in various versions in post war tanks. The 3.7 inch didn't cross over to anti-armour because of the existence of the already very good 17 pdr (76.2mm). It was experimented with in the ground role as the 32 pdr anti-tank gun.
I think that you have to look at the 8.8cm Flak used in the anti-armour role as an emergency response to the inadequacy of early version German anti-tank guns (the 3.7cm, 5.0cm) until the arrival of the 7.5cm, in large quantities, and purpose built 8.8cm anti-tank guns. In the latter part of the war the original Flak 8.8s were employed mostly their anti-air role as Germany was swamped by tactical and strategic bombing campaigns. The dreaded "88s" that the allies encountered when they hit Europe were by that time mostly purpose built 8.8cm Pak versions and often the mistaken, but ubiquitous, 7.5 cm Paks.
The point here is that while the 8.8cm Flak initially served well in the ground role, it was eased out of the dual role (albeit never completely) as better more purpose built systems came on line.
It's the same for modern weapon systems. Air defence systems for the most part are highly networked and integrated systems that depend on a number of ancillary equipment such as radars and computer systems that deconflict weapon effects from friendly air resources. Anti-armour systems, not so much. They're basically cheaper, are probably better served with a separate vehicle configuration, and that's even before you get to the very different tactical deployment of the systems and the skill sets required of their crews.
