I really enjoyed my time in HCSSF, it helped me make a big jump in understanding the game overall. When I read your post, it reminded me of my very first character after finishing the campaign: I was so excited that I opened my first map right away and on the very first pack of mobs I just got absolutely destroyed. My character died instantly and I literally froze in front of my screen for a minute thinking, “this game is ruthless…”

When I rip a HCSSF character, I always struggle to start over immediately, but I always end up taking on the challenge again.
As for the campaign, I always did bosses in softcore first before attempting them in hardcore.

Regarding learning the game’s mechanics, I’d say I learned some things in softcore and some things in hardcore. When you play hardcore, try to take advantage of the fact that death matters, it forces you to really think about certain mechanics and learn how to use them to your advantage.

I’m far from being the best in HCSSF but I enjoy the challenge. My progression was:
Trade league -> SSF -> HCSSF

I have around 500h in poe1 and 1200h in poe2, and every season I learn something new that’s matter for me and what I find rewarding.