Theory: Pyke was designed mainly for autofill assassin mains

Think about it. This is Riot's list of classes:

Type (Subtype) -Tanks (Vanguards, Wardens) -Fighters (Juggernauts, Divers) -Slayers (Assassins, Skirmishers) -Mages (Burst Mages, Battle Mages, Artillery Mages) -Controllers (Enchanters, Disruptors) -Marksmen (Marksmen)

Of these, there are only 4 subtypes which have no direct representation among the support picks(before Pyke): -Artillery Mages -Skirmishers -Assassins -Marksmen

Of these four, three have no similar but different typed champions to play in the support role: artillery mages at least have lux to fall back on. Ashe is the closest you get to marksmen support and, well...that's not gonna fly above mid-bronze. They're the only ones left to dry, but at least they also know more than any non support main what supports actually need to do. It's also worth noting that support is the only spot on the map that doesn't allow for basically every one of the champion types, with the exception of marksmen who have been completely set aside as a class and spot unto their own.

Pyke straddles the line between assassin and skirmisher: his passive adding AD and general mobility/stealth are suggestive of assassins, but the execute auto-killing anyone under the threshold regardless of defenses is more slayer-ish (For reference, Fiora is considered a prime slayer example). The skills of either playstyle will help in your use of Pyke.

Pyke gives zed/yasuo/talon/etc mains a way to continue playing the game they like the way they like even when pushed into a role they would otherwise despise, and often throw*.

*they don't have to mean to, but we all know what having an autofilled support or jungle can do to your team