In the 1970's, when the future air force structure was planned, the "base-line" ground attack force consisted of AJ 37 Viggens in the heavy attack role and Sk 60s in the light attack role.
As the JA 37 fighter version of Viggen was then just starting deliveries, and the last to be delivered in 1990, the need for a replacement in that role wasn't seen as necessary in the same time frame as for the attack force, so when looking at alternatives, it was primarily a ground attack platform or platforms which was desired.
The "natural" replacement for this combination was the A20 Viggen + B3LA. A20 would be a development of JA 37, but with aerodynamic refinements like all moving canard and probably even more parts replaced by composites. This would give the same level of capability as the base-line.
For economic reasons, a slightly lower level of capability was suggested, consisting of upgraded AJ 37 Viggens + B3LA.
In order to save more money, an even lower level of capability was proposed, consisting of only A20 Viggens.
An even cheaper alternative was desired, (even though it would mean even less capability) so the A 38/Sk 38 solution was proposed. The A 38 was a dumbed down version of B3LA with less capable avionics, Sk 38 a trainer version.
The government wanted to spend even less money, so finally the Sk 2 was brought out: It would have been a smaller and cheaper trainer than Sk 38.
As this would not at all give the required capability, foreign alternatives were studied.
The F-16 was studied and was found to basically be able to fulfill the ground attack requirement, the emphasis being on beating back a sea borne invasion with anti-ship missiles. On the other hand, as an interceptor it would just barely do, as in 1980 it took 3 minutes to start an F-16, while the requirement for Swedish fighters is that they are airborne after 60 s from a start order.
Also the F-18 satisfied the ground attack requirement and perhaps also fitted the Swedish profile with dispersed bases somewhat better.
In both cases, they were primarily intended to replace AJ/S 37 Viggens in the middle 1990's, with most likely another fighter bought to replace the JA 37 Viggens a decade or more later.
Shortly thereafter, it was shown that it would be possible to, for less money (comparing to F-18 and assuming a number of 240 or more airframes) develop a true multi role fighter, which eventually could replace all Viggen versions; And Gripen was born.
Mission radius for Viggen: about 1000 km; for Gripen: about 1500 km, presumably not for the same payload.
Payload for Viggen:
Anti-ship missions: 3 x Rb 04E @ 620 kg = 1.8 ton;
2 x RBS 15F @ 600 kg = 1.2 ton;
Bombing: 4 x Mjölner @ 600 kg = 2.4 ton.
For the later alternatives add a circa 1200 kg external tank and you end up with the published figure of 3.6 tons.
I know the JA 37 Viggen has a sometimes published max take off weight of 22500 kg, but that seems to no longer be an official number. Even if it's theoretically possible, what would the load consist of?
For Gripen:
Anti-ship missions: 2 x RBS 15F @ 600 kg + 2 x
Maverick @ 250 kg + ECM pod @ 300(?) kg = 2.0 ton;
Bombing: 2 x Mjölner @ 600 kg + 2 x M70 pods @ 370 kg +
ECM/FLIR pod @ 300(?) kg = 2.2 ton.
Add to this a large
external tank + 2 x Sidewinder and you reach 3.6 ton.
Probably not by coincidence, but by requirement.
And that's not all: You can fit three large tanks, in themselves 3.6 ton, leaving 3 pylons in the 350 kg+ class free, in addition to the wingtip rails = about the 4.5 tons or so needed to attain the published max take off weight of 12.5 ton.
I'm willing to bet that for the "design mission" of 2 x RBS 15F, range is certainly not smaller for Gripen. For other types of missions, Gripen, by having three wet pylons affords greater flexibility, allowing you to take a single RBS 15F or Popeye 2 farther than a Viggen ever could. While carrying more "support equipment".