Who fucks.

singed should be getting his dick wet in the most despicable ways

When Jayce is especially good and clever his reward is to read the princess her bedtime story. Singed unironically thinks this is a good reward and its sweet how excited Jayce gets. Jayce also thinks its a good reward. Viktor is just a little guy he can't unpack all that.

Singed even has a beautiful girl in a magic glass coffin like a fairy tale! Jayce is going to help him save her! How could Viktor say he's bad?

And Viktor has had his falling out with Singed but meets Jayce while he's collecting those plants and recognizes what's going on but Jayce isn't listening.

So he's much easier to manipulate than Viktor. Also just orphaned and still confused about the mage not helping them more so poor little guy gonna be the new magician's lab assistant. If anyone's going to buy the magic through science stuff it's Singed.

So there's so obviously a link between Shimmer and the Arcane, the lab in 1x02 Silco meets Marcus in is covered with the growths that are all over doomed Piltover in the future, that stuff makes you more open to magic or something. And little Jayce loves magic and also trusts strangers too easily.