Changing CentOS in mid-stream

To be more accurate, YUP is from Yellow Dog. Yum although it shares some history with YUP is significantly different and originated from Duke university with Seth Vidal as the primary developer. Technically, similar to dpkg vs Apt. As you noted, just a higher level tool - I consider this as a package manager vs higher level dependency resolver (in Dnf - there are multiple libraries that handle different aspects and the resolver logic is part of libsolv - Originating from Opensuse). In Debian, there have been different resolvers in the past (Smart for example - Canonical at one point was considering making it the default resolver for Ubuntu).