Look, they're the main characters of the story, they're supposed to look badass sometimes..

No party is immune to 100 twig blights in close proximity.

Plus it's just far more fun when players get to actually use the character building decisions they made. I think it's much more fun to base enemy actions on what they can reasonably perceive. If someone has innate fire resistance, let the enemy sorcerer cast burning hands on them once to figure that out. If it's a fabled and well-known Robe of Fire Resistance that they're wearing, any half-intelligent spellcaster will know not to use fire spells on them, but the goblins with flaming arrows might not be so savvy.

Your monk can catch arrows now? Don’t stop shooting them. Shoot them more.

Turn undead and fire spells.

Yes! Shoot your Monk is standard GM advice! they took those powers to look badass, just give them one useless archer per combat and they will shine! And throw arrows!

I can graft parts on my character, so after I put spectator stalks on my head, now all the encounters are summons ️

Monk - *burns reaction catching arrow* Dm - "and now they turn the balista on you" Monk - O_O

I have started to balance the game less and less and its getting more and more fun.

DM- "Catch this, monk boy"

This was always frustrating. One particular dm did that a lot. Oh, x was showing up so someone took y ability to deal with it? X no longer shows up ever again. Cool. Feels bad.

First, hell yes. Second, if you like being an adversarial DM, just let them know that's the type of game you like to run. They don't have to play and you will have to find some players that like that style.

But you see, that's not how 5e works. 5e just throws an endless amount of instant problem solving abilities at your players to the point where there are no problems left except for "How do I deal even more damage?". It still kind of works with characters up to level 7ish, but everything after is just cool character moments without any problem left to overcome. Iean, there's a reason why almost no one plays double digit levels in DnD. I just finished my last DnD campaign and am now enjoying my life with systems that allow me as the DM to actually challenge my players without the need to spend several days of preparation to make sure my encounters won't just be solved by a single "Um actshually..." sentence.

They removed that from monk in 2024

I'd like to imagine the monk catching the ballista projectile and getting whisked away by it

It's honestly really funny to me how frequently some DMs forget basic writing principles. If something is set-up, either by yourself or your players, you should find a way to pay it off. It's a really lame story if your monk has developed an immunity to poison and it never comes up a single time. Chekov's gun was made to be fired!

And if you still want to throw them a curveball you can always throw in the occasional bit of exotic ammunition that messes with them when they catch it (Use sparingly so they still get to feel cool) 

My favorite dragon encounter was a dragon that I still don't know the species of. The damn thing was puce. My DM didn't want us to have any meta knowledge. It was fun though because of how we got to, and dealt with, said dragon. Dragon was in a mountain lair that, when scryed upon it was revealed, was full of traps and minions. My wizard figured out that she had just enough 8th and 9th level spell slots to cast Xorn Movement, and Improved Invisibility on the entire party (no invisibility on herself though), and still have 2 casts of Unfailing Missiles (9th level spell she created). We successfully snuck into the dragons lair, and took positions. Our monk was ready to grapple its tail, our rogue was ready to backstab, and was flying because he had a magic item, our cleric was prepping Harm,and our fighter was annoyed that I put her behind myself. I tapped said sleeping dragon on the nose, and said in Draconic, "Wakey wakey." The dragon opened its mouth to use whatever breath weapon it had, and I said, "That's not a good idea, that will just make me and my friends angry." The dragon then realized I was speaking draconic and parlayed with us. We explained that we didn't even want to be there, but the gods had tasked us with the eviction of the few dragons that weren't supposed to be on this particular prime material plane in the first place. We also explained that we had brought with us 20 empty bags of holding, and would prefer to relocate them off the plane to a plane of their choice. Thankfully that dragon took the deal. The other three ended up with their souls in rather large black diamonds.

Even better, just have that inscribed on the ballista bolt/arrow/the flying tree.

"Oh the monk is immune to poison?! Well hah! ......I completely forgot"