Deadly Strike Works Via Extra Hits

TLDR: see the title?

I've never been 100% certain how Deadly Strike works.  Does Deadly Strike multiply an "existing" autoattack hit, or does it provide an extra hit that is multiplied, the way that Slowdown and Heavy Blow work?

I did a test last year that seemed to indicate the latter (extra blow), and since the other two talents work that way, it makes the most sense to me.  But it's better to have a rigorous test.

Since I have some data with Boss3 tests, I figured to test it next.

To test, I needed a hero with both scatter (to stop the boss proccing) and heavy blow.  Since my Harpy Queen has scatter as her talent, and I have already tested her, she's perfect.

To set the test up, I took off her Berserk 4 crests and replaced them with Deadly Strike 2.  As such, we can expect a slightly longer ramp-up time, so perhaps slightly less damage.  However, the difference should be not more than a second or two of damage at most.  A second's damage in the Boss3 test is ~200000 hitpoints.

Now the actual test.  In the previous test, HQ scored 64953661 damage.

Here's the setup:

Test setup.  Pity you can't see the cresting.

And here's the score:

Boss3 score with Deadly Strike

67936102 damage.  That's 2982441 more damage than the original run without DS crests.  Over 175 seconds (this is approximated time of engagement to account for PD having to amp up), it is 17042 DPS.  In terms of extra hits, it is 0.487 HPS extra.  This is almost exactly the 0.5 extra HPS predicted.

Conclusion: Deadly Strike works via extra hits.