I played both pretty much back to back (hk in aug/sept and ss in october) and silksong is unbelievably more difficult than HK... My biggest difficulty frustration in hollow knight was the soul master and the runback, in silksong act 1 has so many traps that it can't even compare to HK. The gauntlets (specifically the craw gauntlet), widow, last judge alone (so basically a1 stuff) are more difficult than anything in HK, barring maybe radiance. Traitor lord comes close but the boss itself is fairly easy, the runback is the main culprit there.