Dota has 118 heroes, not all are ported to Dota 2 yet, roughly 90 have been added. They don't rebalance everyone based on the meta, they tweak them when they're being overplayed or underplayed all around. A change in the meta doesn't require everything being reworked, and it hardly comes to luck when you need to adapt your techniques once the enemy team knows what your routine is.
The thing back in Dota used to be trilanes galore, people always ran them. Once people started using heroes with escape mechanics and long range cs abilities like Windrunner and Clockwerk, people started to realize their trilanes weren't raking in enough kills to be worth splitting the exp 3 ways like that. They didn't completely cripple either of those heroes to make them unable to counter a trilane, they just had players realize this stuff isn't working, so they came up with something better.
It wasn't luck, professional teams do no rely on luck to win their games. If you think so, you really need to rework your view on drafting. The captains of these teams are professional, they have gone over the combos, lineups, strategies, counters, everything. If people start picking willy nilly with no composition they are going to get facerolled by anyone with half a brain.
Also, if heroes were balanced to only do one thing and just that, it would be extremely boring playing them. Going to go back to my example of Tiny, who was most commonly played as a burst damage hero using his spells. Around TI2, EHOME was making him do burst damage with his physical attacks because of how good his upgraded ultimate was, so giving him more farm than they usually do let them completely rework the hero without actually changing his mechanics at all. That's good balance, and also creativity/being able to break the meta. A permanent fixed meta is a terrible thing and I'm getting tired of trying to get it through. If your meta can't be changed and things are solely built around it, that's a big balance issue right there.
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