Getting passed the fifth pantheon in hollow knight has to be the biggest grind I've ever done in my life, beating grim was no easy feat, it took me 3 hours straight of grind, but beating every single boss of the game, in a row, without dying... my god, it took me at least 30 hours to accomplish that, you have to learn the attack patterns of every boss if you want to stand a chance, but the cruelest part were the last 3 encounters of the boss rush, first it was Grim, again, the boss that took me 3 hours to beat, now I had to beat it him without dying, second it was the pure vessel, very quick and unforgiving, deals two hearts per hit so you can't make many mistakes, he sent me back to the start countless times, and the last one, the hardest of the three: Absolute Radiance, it's a 7 phase monstrosity and if you die, it's all the way back to the start, 40 minutes of bosses just to make it back to Absolute Radiance, I had to redo these fights so many times, but eventually I managed to do it.
Silksong's base game may be a bit tougher overall than the og hollow knight, but the og hollow knight definitely has the hardest extra content, at least for the time being.