AGPLv3 attempts to solve this problem, by forcing SaaS providers to open-source their modifications.

https://www.gnu.org/licenses/agpl-3.0.en.html

Depends on the needs of the licensor. AGPLv3 solves the problem of other players taking the code, improving it privately, and not sharing those improvements. But AGPLv3 is not a silver bullet for people who write Open Source code and pretend to make a living from it. "Open Source is not a business plan".

https://news.ycombinator.com/item?id=45095581