Customize CRM Online in newer versions is extremely slow, new versions have higher latency to load forms, entities, fields, views, etc.
When customizing and publishing solutions in CRM Online time compared with Onpremise versions is above 5x Onprem time.
Developing in CRM Online has becoming time consuming and stressful
System customizations windows takes a long time to open even the rest of the system is normal
Doing first customizations now is more time consuming and stressful
Keep customizing CRM Online to add or modify even a field or view takes more time now and generates bad experience overall
This affects developers and partners that work with CRM Online and transitions from CRM Onpremise to CRM Online when versions are different and it is not possible to migrate them directly
Your day could be broken just because a new field needs to be added and takes a lot of time to customize the form and publish changes, and changes that could take hours now takes days to perform
Hope future versions could have better performance or less need of time to customize CRM Online