I'm currently into a migration SharePoint 2013 to SharePoint 2019. The customer (and this is no exceptional case) wants to stay onPrem...
Therefore I can compare both worlds onPrem and online there is a huge count of web parts, features, etc. missing for local installations. And the gap keeps on growing.
Is there anything announced that onPrem customers will get "Feature Packs" or "Feature Updates" to keep it as near as possible to SPO? I'm aware of that not all features will work (connection to PowerBI and other online services) but there are improvements that are kind of critical, like way greater configurations for web parts, the ability to set links on images, improved copy/paste behaviours on pages, and so on.
If this development keeps on going, I fear that most of onPrem customers will not go into M365/SPO but to another provider which supports local installations.