I got really long winded on this one sorry. TL;DR yes it would be easier for a big company’s IT department to handle rolling their own nextcloud but larger companies also have more obligations that make it a bit more complicated. A smaller company will need less compute and storage and manhours to manage a next cloud instance and so they can get away with it if they have a great IT person/staff
An on-premises deployment is going to take more manpower to support and maintain than a cloud deployment and an organization of 200 like OP is probably going to have 5-6 IT people who are already stretched thin.
And cloud storage is definitely a cost just like on-premises but it also comes with SLAs with guaranteed uptime and has factors of scale to be able to make delivering uptime, performance, security, and updates a lot more cost effective than rolling your own nextcloud. I’m sure it can be done in a way that is cheaper than $4000 a month or whatever 200 workspace licenses cost but not without taking a shortcut. I wouldn’t run it without a dev, prod, backup and DR server and the salary to maintain those would be just as high.
I’m making assumptions based on my experience and organization’s size and making an educated guess about his friends situation. It could be totally different and they could still have capable hardware and storage from before their cloud migration. I just know that if I was in the same position I would not want to be the one in charge of rolling the company nextcloud when down time is money lost.