Yeah, HK is a huge game and Silksong is probably bigger; it'll take a while to play through both. But that's a good thing. Play these games for the experience of playing them, no need to rush through them just to check them off a list.
There's nothing wrong with using a guide if that's how you have the most fun. But I think most people would have more fun playing Hollow Knight without one, which is why I don't think "if you [play Hollow Knight], use a guide or something" is good advice as an unqualified statement. I enjoy the experience of playing a game far more than the accomplishment of having completed it, so I'd rather enjoy a game fully and leave it unfinished than halfheartedly rush through it with a guide.
So, yes, I probably should have qualified my statement.
I meant this more if my parent wanted to get through Hollow Knight quickly, as a gateway for Silksong.
I say this because just thinking about playing Silksong immediately after finishing HK made me feel exhausted.
I wouldn't recommend playing HK in this manner though; it's more fun to explore, and use a guide only if you really hit a wall.
So, yeah in hindsight probably bad advice even after qualification.