In dnd, I'm planning on playing a fighter/sorcerer with divine soul (giving me access to cleric spells) and battle master, essentially having the ability to be the active person in the group (I call it the "holy errand boy") however, during theory crafting I found legendary weapons and figured "if I can take the form of any weapon and it's effects if it's associated with a deity, then what about weapons like Defender which is stupid versatile or Luck Blade which according to CBR is the best weapon in the game apparently?" I'd love the ability to conjure Luck Blade and have access to wish for about 60 seconds and get the real thing, but that seems incredibly overpowered and WAY too good to be true. Is it?
The spell does what the description says it does.
The spell description tells you exactly what the effect of the spell is. The rules for Spellcasting state:
Each spell description in Chapter 11 begins with a block of information, including the spell’s name, level, school of magic, casting time, range, components, and duration. The rest of a spell entry describes the spell’s effect.
Spiritual weapon tells you what it can do, and what it can do is create a weapon that resembles a certain weapon:
The weapon can take whatever form you choose. Clerics of deities who are associated with a particular weapon (as St. Cuthbert is known for his mace and Thor for his hammer) make this spell's effect resemble that weapon.
It can resemble a particular weapon, but only has the effect of the spell, not any affects the real version of the weapon may have.
And for a bit of general guidance, if your reading of a 2nd level spell (spiritual weapon) allows you to recreate the effect of a 9th level spell (wish), that should give a strong indication that you’ve misunderstood something