Hi, yawfle!
My name is Anna, and I’m a mapper on the OSM team at Lyft. Thank you for paying attention to this. You are absolutely right, removing a mentioned segment could block traffic for cyclists.
In order to more reliably block unwanted routing at this intersection, let's inspect one of the following options:
1. We can add the tag motor_vehicle=no to the segment with barrier, that will block car routing;
2. Based on your knowledge that the cycle and emergency traffic is allowed, we can add a combination of tags to the node with planter: access=no + bicycle=yes + emergency=yes.
We will be glad to know your opinion on this matter. 
Best regards,
Anna