Civ-Combat is not about realism, it is about math
on a site note, Im not military personal,
but do you think the small M6 Bradley 25mm Autogun (cant realy effectivly fire a Stinger on a Tank) could penetrate though 150mm Tank-Steel (as example Panzerkampfwagen VI Tiger II, not some Sherman), I hadly doupt
on the other side, a 88mm Tank-Gun could penetrate though 180mm tanksteel on a reasonable range
the M6 lacks some serious Anti-Tank weapons and its main usage is support for Tanks in order to combat drones, gunships and cruise missles, it is not designed to figth tanks. Mech. Inf. has a similar concept ingame
Im sure the M6 chance would be better just for the reasons of speed, posibility of faster maneuvers, communication and precision but I would not underestimate "old" things
If they are used from someone with several years Combat Expirience compared to a greenhorn thats just from military academy things change even more.
as I said, civ is not about realism, more about math ... but dont underestimate something just because its "old" and not high-tech
in fact a old Messerschmitt has a higher chance to combat a Stealthbomber then a modern Jet, as modern airplanes rely much on their electronical detection while those old planes were just used by looking for the enemy with your eyes (and its easier to see a Stealthbomber while it is aproaching the area (lets say factory) you protect, then detecting it with Radar)
same goes with AA, old Flak Guns have a better chance to destroy a Stealthbomber then a Radar-Guided-Missle (which cant detect, so it wont even fire) ... with a flak you just put out some curtain fire and you gain a chance to damage the attacker
things arent allways black & white ... alot of times its grey