try vs catch unreachable compares two different programs

Add allocators to the list of things held equal. One candidate reuses a dynamic array across batches. The other builds into temp storage and clears it after every batch. Same inputs, different storage lifetimes, and the timing absorbs the difference without saying so. The array also keeps whatever allocator it was made with, so switching the context between runs does nothing for it. Write down which allocator each container holds and where the clear happens. That belongs in the workload description whether or not allocation ends up inside the timed region.

The ownership requirement in your list should cover the failing run as well. An operation that acquires the first buffer and then fails on the second has to release the first before it returns the error. Both candidates must do that same work, or the failure measurements compare different cleanup.

One C rule tends to get stretched here. free(NULL) is defined to do nothing. That rule covers a null pointer and nothing else. Releasing the first buffer twice is undefined behavior, and no null check can tell a valid non-null pointer from one that was already freed.

And if either allocation can fail, valid inputs are no reason for catch unreachable at all. try hands the error up and leaves the first buffer allocated, which is the job errdefer exists for.