Nightmare has it right. Daywalker build is:
BA 2
BB 12
Flurry 12
Meta 12
Sprint 8
TP 4
I think the attributes were
Con 6
Wis 2
Str 2
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The idea is to use BB+Flurry combo to do damage while having Meta on so it heals you at the same time. TP for interrupt (4 instead of 1 to get some range and a bit area damage), Sprint for movement (which is very important for the build, since this a blitzkrieg build - basically, go in where you're needed the most, flurry and go out; also, having sprint on while flurrying helps to keep in range so the target cannot so easily interrupt the flurry by running) and BA 2 so you can fight against those tank reavers and have a chance.
There's a huge difference between having a BA and not having it. BA 2 is 10 damage, whereas BA 12 is 20 damage and no BA is 0 damage. When fighting against a tank with BA 12, taking 20 damage for each hit you make is nasty. If the other guy takes none for each his hit, you're gonna lose. If he takes 10, you have a chance.
It's also a psychological weapon. People don't like to hit BA reavers because they take almost as much damage as they give. Also, in game people don't typically know your BA level, so they sometimes treat your BA 2 as if it was BA 12

It's also good when you need to sacrifice yourself for the team. At least you'll be doing some damage while getting ganged.
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I would've loved to have Sprint 12, but I liked TP 4 more. One tweak that is possible for this build is to reduce BA and TP to 1 and have Sprint 12.
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5 I KNOW he had Whirlwind, because I remember him whirlwinding around our portal at a few GvG's
My other reaver build has Whirlwind, but I doubt you've seen that in GvG since it was created after official servers went down.
Anyway, now that I've tested it I'd still go with no WW build. WW is good, but not that good. I'd say an optimal team has one reaver with WW and one without.
6 I KNOW he had BB because he loved that skill (and I remember myself frowning at having BB and BA in the same build)
BB is perhaps the best reaver skill, and one of the best skills in the game after Bombard and some others. And the combination of flurry/whirlwind, BB and meta is a lethal one. I prefer flurry over whirlwind because it does more damage and that way ends up healing me more. Surprisingly, simply doing normal hits with BB on ends up giving almost as good heal, due to the speed boost.
I suppose you were frowning because BA reduces attack speed while BB boosts it. However, I tested the build without BA. In fact, it originally had TH instead of BA, since 2 interrupts is always better than 1. But without BA, it was totally impossible to fight tank reavers, although I think back then BA gave armor boost as well. I tested going without BA again when armor boost was removed, but still found the passive damage to be better.