I felt that its upgrade "Genocider" was perfectly fine. I agree on the others, though.
That's fair, I was looking at it from the viewpoint of doing normal difficulty missions where you just don't get the opportunity to turn around and use it. Once you've unlocked the shop and can get speed upgrades, it becomes a very high dps weapon that doesn't struggle.
Do weapon upgrades need certain utility selections to be selectable in this game? Like in vampire survivor you need the spinach for the fire wand. If so, does someone know which ones?
Yes, you can check in the arsenal for that information, it's the 3rd option in the selection screen. Every weapon will tell you what you need to upgrade it. 1st Row is weapons, 3rd row is the passive it needs, and 2nd row is the item it upgrades to. Just like VS they get extra abilities and then you can also level them up 4 more times for additional damage increases. Molecular Blade gets a full circular AoE and hits 3x, Assault Rifle has virtually no cooldown, Defense Radiation gets lifesteal on kill, Autocannon gets like 6x more bullets fired in an multidirectional spread, etc.
I'd strongly recommend the Empty Blade in every run until you have all 6 weapon slots and passive slots unlocked for a character, it's almost impossible to clear most missions otherwise.