If you promptly shut off the other engine, does it become equivalent to single engine failure?

Not really. Twin engine aircraft don't have to meet the same crash worthiness standards and usually have higher stall speeds (in this case minimum crash speeds).

To be fair the statistics are swayed slightly by a number of factors, training accidents and different risk profiles of the flights.

In general, a twin will weigh considerably more than a single as well as having greater drag, making for shorter glides.