Even with a CLA in place, you can still fork, improve and sell Synapse / Dendrite (or derivatives of it), as long as you follow the AGPL.
The very existence of those forks breaks the community's ability to truly collaborate. Private forks still participate in our ecosystem!
This means that the only effective result of switching to the AGPL is that Element can demand money from anyone who makes a proprietary fork. Basically, the AGPL has been backdoored for profit.