F-16A's with a PW200 engine and 23,900lbs of thrust compared to the F-16C's GE129 engine with 29,500lbs of thrust is a pretty big difference, almost 6000lbs, which generously offsets the weight difference between the two blocks. The DCS viper's flight model is being questioned because it doesn't line up with EM diagrams, and is still in early access. ED also agrees with this and has stated that they are going to refine it. It has nothing to do with a certain block being a 'sead variant' or a 'ground attack variant'.
Block 40/50's were being developed in the mid to late 80's BEFORE the soviet union collapsed, with the block 50s rolling out in 91. The fall of the USSR has nothing to do with vipers gaining weight. Its because of new avionics being added as technology advances. If you want to compare the DCS vipers' performance to a real life one, look at the HAF viper with conformal fuel tanks.
That being said, I would absolutely pay $60-80-whatever for an F-16A for all the reasons you posted. No datalink, no aim120, primitive cockpit, and maybe a chance of ED adding the B61 . Maybe a 3rd party could develop it instead of ED considering their workload, but honestly it probably won't sell as much as an F-4 or F-111 or whatever is next down the pipeline.