.deb has epochs too, but I think Debian developers avoid it where possible because 1:5.4.5 is interpreted as newer than anything without a colon, so it would break eg. packages that depend on liblzma >= 5.0, < 6. There may be more common cases that aren't coming to mind now.
Seems like debian is mixing too many things into the package version - version used for deciding on upgrades and abi version for dependencies should be decoupled like it is in modern RPM distros.
If a binary library ABI is backwards-incompatible, they change the package name. I was just guessing at the reason epoch is avoided and that <6 is probably an awful example.
So now I actually bothered to look it up, and it turns out the actual reason is that the epoch changes what version is considered "greater", but it's not part of the .deb filename, so you still can't reuse version numbers used in the past. If you release 5.0, then 5.1, then you want to rollback and release 1:5.0, it's going to break things in the Debian archives. https://www.debian.org/doc/debian-policy/ch-binary.html#uniq...
