That's like getting only the first ending in Hollow Knight and never awakening the Dream Nail. There's some pretty significant stuff left...
Also, I don't really blame you. I found Act 2 challenging, and it just got harder from there. Act 3 was brutal.
Some things you missed out on:
- three gauntlets back to back with no bench
- at least 8 boss fights, including...
- possibly the hardest boss fight in the game
- the other hardest boss fight in the game
- possibly several optional areas plus at least three[1] definitely missed areas -- and the bosses/quests/challenges associated with them
- at least one crest
- at least one movement ability
...among other things.
[1]: Not sure on the exact count on further reflection; may be more depending on how you count areas.