Yes, and that complaint is specific to Unity's current GC. They will update it eventually, and it will no longer suck.

Does the GC in Unreal-mono have the same problems? If not, it's a non-issue.

It should be significantly better, but can still pause. Beyond this, it really depends on how you are allocating/using/reusing objects... There are techniques you can use that aren't too painful to overcome some of the issues.

Unity has a specific situation with Mono that doesn't apply to anything else. It won't apply here, something like this can use the latest Mono.

The concurrent GC in the latest .Net still requires pausing (though the time is less), because the heap still requires compacting, and no code can run while that operation happens.

Invoking the GC constantly on a frame by frame basis can quickly lead to heap fragmentation, resulting in pausing, because that is considered 'working against' the GC (both stop the world and concurrent). This is where custom solutions, such as pooling, should be used to mitigate these issues.