WetGeek Why install files from an .ISO and then need to immediately replace them with an update online?
The only distro that I have ever installed without immediate post-installation updates is Ubuntu Budgie 22.04 LTS, which I installed the day on which the ISO was released. Within a week, the updates started to come down, and I'm betting that when I install from the ISO on another computer next week, at least 100 files will update after installation.
It is definitely time for Solus to release a 4.4 ISO (my preference would be a new ISO every six months, say April and October each year to line up with static ISO releases) but it would be a matter of just a few weeks before several hundred files would update immediately after installation from an ISO, and the installation-update-complaint cycle would begin again.
The need for scheduled and relatively frequent ISO releases is driven by the need to keep the kernel and drivers up to date, as others have pointed out, and that is why it is time for a new ISO.
Edit/Update: In support of the suggestion that rolling release ISO's quickly become outdated, I note that this week's update consisted of 97 packages on a Solus Budgie out-of-the-box (no apps added except Steam, which updates independently of the distro, and Keepass, which did not update) installation.