You might think so, since when we see that in the scheme there is a Main Maintainer and 4 other categories of Maintainers, there are the collaborating developers, that is a core of work.

But the implementation of a major and irreversible modification of the software is subject to approval by the nodes and support by the miners.

In the case of BIPs, it is proposed by any developer, it is debated, a draft is created and this must be approved by the maintainers. The debate is public on GitHub. It is peer reviewed on GitHub and other ways. Then it is implemented.

From this we can conclude that in their role as code maintainers they only have some degree of responsibility. But in no way are they a threat to centralization.