Swingarm is responsible for keeping everything in align and allow free movement in only one plane, the shocks and springs only carry the live load (your bum) and in practice less then half the weight of the bike (unless you pop a big ass wheelie), top eyelets on the originals are probably even rubber so they do virtually nothing to resist lateral movement. The drive train (chain) and rear brake actually impose some of the highest stress loads that the swingarm will ever need to contend with....
On the basis the original twin shock set up has 4 non-rigid links (2 top and 2 bottom of shocks), and the shocks are inherently 'flexible', are they adding any strength to the swing arm?
Or, does the swing arm rely entirely on its own integrity to resist twisting at the axle?...
Which brings up another area of concern; you can beef up your swingarm all you want but the rear hub on your bike is not particularly strong by design, you have a skinny steel axle fitted with 2 light duty roller bearings worth (about 4 bucks each) pressed into an aluminum flange that is far from optimal in its design (light duty bearings not widely spaced apart and rubber cushion drive in the hub)
lol Toni Bou would destroy that in about 10 hops, even I have completely shattered better designed hubs then that one on an MX bike.
Modern hub off a 150 pound trials bike that has about half the horses, larger bearings, fatter axle, widely spaced bearing races and superior angle on the spokes for visual comparison.