It's not always like that though.
Some players just dont want to use the "usual" builds for a variety of reasons. Maybe they disagree with the whole thing, maybe they've found a build that works well for them specifically. I think most of the time it's not just done for teh lulz. It's just the player in question doing their role in their own way. It's what I typically do in.... pretty much everything in every genre. I never get anywhere otherwise.
Of course there still are indeed plenty who will purposely choose specific setups that will ruin things, because "HUR HUR DUR THAT'LL SHOW THOSE N00BS", but they're often alot more obvious because they'll be acting like morons in the chat and such.
....and in Wingflier's case here he did kinda get 10 bazillion kills, so it seems to have worked out fine.
True enough. I generally go out of my way to build outside the "popular" builds, mostly because I hate being generic. But there are things you just don't do because they're pointless and directly detrimental. Hastened Fatalis is such a case. It's a scarce number of gods on who it can technically work, and even fewer where it's actually a good idea. Never get it on a hunter, for instance. Most assassins are also ruled out because it hurts their damage output too much. Kali and Osiris can build it to get sticking power, but Kali can just build Sprint, and Osiris has a bajillion slows so he doesn't really need it either.
On Bastet it's terrible because she really doesn't use her basics that much, she has a slow, a speed steroid, a jump and is more of a physical caster (meaning she needs CDR and penetration) than an AA-god. So it really rubs me the wrong way when people build items that are clearly detrimental to how the god is designed. It's like building auto-attack items on someone like Vulcan.
I personally build Hastalis on Poseidon sometimes (in addition to other AA-items). Now, Poseidon is generally a burst mage with HUGE damage output, but with his steroid, movement speed and insane sticking power, you CAN play him as an AA god, but it's just not as good as burst mage. But few people expect it so they end up boxing him and dying horribly
But yes, naturally Wingflier got a bajillion kills. He knows MOBAs, he generally knows how to play even though his builds may be strange. Bastet is a god with high base damage so even IF you build her awfully, you are going to get a lot of kills from her base damage alone. Especially if your opponents are more clueless than yourself ^^