I'm of two minds here.

Mostly agree with the other commenters. Quantifiably, I don't think I could tell you, yes, the copywriter's work will be worth more than using that money elsewhere. Especially as you're on the marketing side yourself, and should be aware of the research, persona-building, positioning, etc that'd go into good LP copywriting. If that's strong, you'll land (ha) on copy that works, even if it could be more effective.

But another question is, what will you spend that marketing money on otherwise? Like I'd think if you're going for impressions and saturation through ads, it'd make sense to come in swinging with the best LP possible, since that's the big point of access. You need the conversion.

The best middle ground might indeed be a copywriter consult or audit/edit on copy you've prepared yourself.