Can you explain more what you think is unfair about the test? I've only given it[1] a brief read and it certainly is a synthetic benchmark, but it doesn't seem absurdly artificial.
I've certainly written JS that builds trees, modifies them, tears them down, and builds new ones, all within the same event loop turn, and so would certainly benefit from incremental GC in the cases when the data it's working over is very large (or it's just a part of an app that's already been burning through a large number of allocations).
[1] https://code.google.com/p/octane-benchmark/source/browse/tru...
