That's a unique weapon...it's not something that allows you to use even all rapiers or anything like that. And you still need the relevant weapon proficiency to use it which wizards typically don't have as it's not a simple weapon. You might try to go for a specific race just to get that proficiency to nick that weapon off Wyll but really it's not worth it...if your plan is to have your wizard in melee range of enemies you're screwing up.
Most common race for Wizards / Sorcerers in BG3 is various forms of elf, most if not all of them grant rapier proficiency.
Melee Wizards were quite incredible in BG2 and most other DnD games, another thing that BG3 handles poorly. It wouldn't be anything different to using wyll as melee while hes a warlock, all you needed was polymorph self or tensers transformation.
Eldritch Knight in previous DnD editions was a wizard prestige that allowed the use of INT for attack rolls and damage while having the same amount of spellslots as a normal Wizard, but Archmage and Pale Master remained better for actually casting spells.
But regardless of that, that rapier raises spell save DC, its good to nick just for that.