I was fortunate enough to use lisp professionally for nearly 20 years. The only reason that gig ended was the unfortunate demise of the majority owner and founder, and his heirs selling the shop to a competitor that only wanted the customer database imported. Lisp was never the problem, nor particularily messy.

On the contrary, we considered it a major reason we were able to build a quite successful stock broker and bank from scratch with a team of 4-6 people, who doubled as datacenter ops (we ran on-prem), internal tech support for the rest of the firm (~20 people) and 2.line customer support.

We quite naturally converged on a set of internal libraries for various tasks. Understanding and fixing each other’s code was not a big deal.

Coincidentally, our frontend was php. That was messier, and we conciously kept that layer as lean as possible.