League of Legends (LoL) Question: Why riot nerfs weird builds ?

Creativity requires that a lot of different options are viable. When one champion with a particular build is significantly stronger than everyone else, that's not creative. Everyone doing the same thing because it's ridiculously strong is not creative. If you want creativity, you should be happy that Riot does a good job of nerfing the strongest picks and buffing the weaker ones.

if riot did not nerf these champions, they would be broken and simply rule the current meta. AP tryndamere was simply much too strong in lane, and out of lane as well. The spammable 1.5 ap ratio heal is really broken, so they nerfed it. Now, you cannot rely on it to keep you at full health.

Rengar heal was the same thing, and rengar could use his roar at 4 stacks, then roar again with 5 stacks, dealing 2 1:1 ratios. 1:1 ratios are overpowered already, so that is why they nerfed it.

Actually, Riot 100% supports nonstandard builds; several staff members have said such. The problem is they were too powerful that they were breaking that character's purpose. Most of the time, those ratios were there to support maybe 1 nonstandard item to buff that skill or provide damage deviation (so if the opponent builds armor, you can still provide magic damage, etc), not a whole inventory.