The end of the quote I provided does some very high level contrasting of the well known RoCE v2 RDMA over converged Ethernet, which is the most popular IBoE like thing.

I'm sure there's a lot more nuanced to it all. But I think predictability/utilization/latency in RoCE are worse, that it relies on Explicit Congestion Notification more for flow control. Where-as UE is using Infiniband style credit based flow control, which should insure that any data sent has sufficient throughout allocated to it to be received.

UE seems to be a more direct creation of an Infiniband like network, atop Ethernet but where all players are agreeing to behave in an Infiniband like way with Infiniband predictability, where-as RoCE encapsulates Infiniband data but still behaves more like an Ethernet network lacking the coordination of Infiniband. I'm far from certain; it'd be so fun to have some extensive material to go over to really find out.