Lead conversion requires create and edit permission on Account:
To convert leads:
Create and Edit on leads, accounts, contacts, and opportunities AND Convert Leads
You will not be able to completely remove the ability to create new Accounts while also preserving the ability to convert Leads.
The route that seems most plausible to me would be to write a Validation Rule on Account. Something like
AND(ISNEW(),
NOT(ISBLANK(LeadSource)),
NOT($Permission.Some_Custom_Permission)
where you'd create a new Custom Permission that allows the creation of new Accounts and add it via Profile or Permission Set to those who should be allowed to have that privilege.