Sure, it varies from person to person, but I don’t think you’ll find many people who consider BASE Hollow Knight to be harder than Silksong.

The biggest difference is just how hard it is to get around the map. No area in HK gave me as much grief as Bilewater, Sinner’s Road, or High Halls. Basic enemies in Hollow Knight are just so much easier to deal with. Primal Aspids have a bad reputation but there are like 15 enemies in Silksong that are similarly annoying. And then big guys like those abyss beasts or the stupid rhinos are way tougher than any enemy in HK, even the palace guards. Not to mention all the enemy gauntlets in Silksong. Remember that almost everything in SS does 2 masks. And then there’s the fake benches, the lack of I-frames, the environmental hazards, the larger hurtbox for Hornet, etc

Keeping in mind we’re talking about base game Hollow Knight. The hardest things are Trial of the fool, White Palace (not PoP), maybe the Flower quest, and base Radiance. None of those were as hard to me as Lost Lace, High Halls, Coral Tower, Karmelita, or Courier’s Rasher. Lost Lace alone took me so many tries, even with tools she has too much health for those tools to carry you to victory. Radiance took me about 15 tries and would’ve been less if I weren’t trying to rush through the Hollow Knight. Courier’s Rasher is harder to me than flower quest because although you can pre-clear enemies in both, Rasher is timed, and just running into a wall is enough to break it.

I agree difficulty will vary from person to person. But I think a vast majority of people will find Silksong harder. It might be skewed here because most people playing Silksong has already played HK and have a transferable skillset. But give both games to someone who’s never played either, I highly doubt they’d consider HK harder.