Most of this is because people don't realize the easiest kill order for bosses. Spellblade Aluriel and Krosus are both much harder than Botanist Telarn. I would expect more people to start going 4/10 Mythic or 5/10 Mythic by doing Botanist Telarn and Krosus now that the doors are open.
Botanist Telarn is a 20-30 pull boss for even "bad/undergeared" guilds, but very few people have realized this and gone to it.
Strawberry Puppy Kisses is 5/10 Mythic and they don't do splits. They'll probably be 7/10 Mythic after their raid tonight or at least 6/10. Splits are not required to be 7/10 Mythic right now. In general, the guilds that do splits also raid more. That is why you see them with more kills. 7/10 Mythic is achieve-able by World top 200-300 right now, it's simply a matter of time spent to get there.