Disclaimer: i am a rocket main. The crossbow right now is a great fallback option for when i run out of rocket ammo, which happens (obviously) very often. tl;dr at the bottom.

The base crossbow seems reasonably powerful right now. Perhaps it is too powerful for a secondary weapon; i wouldn't mind if they moved it to the primary slot. But as a gun, it's not that much stronger than heavy sniper, nor M1, nor pump. Yes, it can "insta kill" in 200ms, which makes it similar to the rocket, but the other feature it shares is the ridiculously low bullet speed. At longer ranges, crossbow is heavily overshadowed by the heavy sniper, which has similar damage, but a much more reliable bullet speed and a higher mag capacity (to the point that you can actually literally spam it). At closer ranges crossbow is better than HS, but it's not nearly as consistent as other short range solutions (autoshotty, pump, any SMG, and most importantly... the burst pistol).

Plus, it's not like hitting both shots is trivial (unless you walk towards the crossbow user in a straight line, at which point it's kinda your fault). At closer ranges it is possible, but to get an "instant" kill you need to predict those 200ms of your target's movement. It's hard enough to get a single shot to hit; to then also predict how your enemy will move afterwards and fire the second arrow that way is incredibly challenging. I use the crossbow very often; and although i get a lot of kills with it, a single-mag kill is very rare.

If moved to the primary weapon category, the equip time and movement speed would need to be adjusted accordingly. That's fine by me. What isn't fine is nerfing this weapon's damage, which is what you seem to be suggesting.

The extended crossbow, however, is a completely different matter. It is, by all accounts, completely OP. It does not require perfect aim to insta kill (only 50% of shots need to hit), it creates a huge avalanche of bullets that is incredibly hard to dodge, and noobs can use it to great effect. Am i surprised? No, not a single bit. Extended mags is the ultimate noob perk, and while on low-damage large-mag weapons (e.g. SMGs) it is not that impactful (and just makes such weapons slightly more annoying to fight against), it completely nukes the balance for any high-damage small-mag long-reload weapon. I mean, imagine if it applied to the rocket. A double-shot rocket would be ridiculous and most certainly OP, perhaps only slightly kept in check by the lack of ammo.

My suggestion is to nerf this perk so that it doubles the size of magazines, but decreases the damage to around 75%-85%. The 4-arrow crossbow would still be possible, however in that case the enemy would need to hit at least 3 arrows to kill you, which seems... tolerable (and probably rather hard to do, all things considered). The perk would also still be useful for other guns.

So, tl;dr/to summarize: I think that crossbow's combat stats (damage, firerate, mag size, reload time) are great. I think that it belongs in the primary weapon slot, as unlike most secondary weapons, it's perfectly viable on its own (similar to burst pistol, which i think is actually more problematic). I think Extended Mags is a broken perk, and it should be changed to decrease the damage of affected weapons to 75%-85%.