Fair enough, I did neglect the silver gains from the additional runs that method 1 does. This is counterbalanced by the higher rarities of method 2, don't know which way it comes out on net. (To be crystal clear: definitely a mistake on my side, thanks for pointing it out!)
I don't particularly think of silver for dragon and IG. dragon gives waaaay less silver than spider. Something like a factor 3 difference. IG is even worse. The only half-decent one is FK. If you want silver, you should avoid the 3 other dungeons as much as possible. That means, going in, reaching your goals, and leaving again. Your goals are either fusions or gear. If you value gear very close to 0, then solo 20 strats are of course correct. But even if you value gear only somewhat, then farming a bit of gear as a side effect of doing the fusion is a good thing.
My account is still at the point where a 6* leggo without set bonus is a viable piece. Of course certain sets are way more valuable than others. That doesn't mean a piece of a "blank" set is worthless though!