Improve the current UI library or build a new one?

I recently joined a company with a small team but not a startup. I'm working on a CRM SaaS product, which has a few years, but it's not very sophisticated (UX and UI wise).

When they started to build the product, the team created a Storybook library with a few components designed by developers. There was no designer in the team back then.

The designers that came to the team after it created many UI Kits but they were never implemented. They used to design the mockups using their UI Kits, and it was up to the developers to decide how to adapt to the already existing UI. In summary, this is what I'm facing right now:

• No UI Kit to work with as a source of truth;
• The current UI Library it's bad (not only the looks but has huge usability issues);
• The mockups needs always to be adapted ad-hoc during the implementation.

I've been thinking of two possible solutions:

• I ignore the current UI Library, create a new UI Kit, and push for a redesign;
• I work on building a UI Kit that matches the current UI Library and improve the components and styles over time.

Both have pros and cons. I'm pretty sure this is something that a lot of designers already faced at least once. What is your experience with this kind of problem? What have you done? What was the outcome?

Thanks :)