That makes more sense than the 8 costed version on Facebook. Still, in the abstract I'd rather have the flexibility offered by Vine Tree, even for 2 more mana. I'll have to try both and see how I like Seedling Pod based play, but that's my reaction just from reading the cards.
Vine Tree only allows Vine creatures/conjurations. Seedling Pods allows Plant creatures/conjurations. Vines are a subset of Plants. So Vine Tree may give you greater penetration but what it produces is less flexible. If Tanglevine remains a Plant only etc.
I can also imagine there are some Plant synergies to leverage in the set as the 2 turn deferred arrival via Pods which actually have less penetration than Vine Tree's double vine growth. For example this "Renewing Rain" that Arcanus mentioned could be an incantation "for each Plant you control in the arena, you may do 1 of the following: remove 2 damage, remove 2 burn or add 2 mana on it if it can channel". With such a spell, the Pod strategy could be even better...
I gather Pods once allowed placement further distance than the "in its zone" version spoiled in the News section. I could have sworn I saw a version that allowed adjacent zones but I may have imagined it. If Pods, like Samara Tree, are not exactly as spoiled in final print, then that may explain the apparent disparity in benefit.
Without knowing just how much of a subset Vines are among Plants, it's hard to gauge. One thing is true. Only a Seedling Pod can use a vine marker to create a non-Vine Plant in a distant zone. Trees cannot be Vines (e.g. Togorah, Lifetree). I'm sure that's worth something.
Still, with the incomplete knowledge caveat, I tend to agree with you that I'm preferring the greater penetration and tempo of the Vine Tree to the slower, less penetrating Samara Tree. However, that's only out of the cards spoiled so far...
I think just as there are (at least) 2 Necromancer strategies so far, Zombie Semi-Recursion & Traditional Undead Army, this difference is highlighting divergent strategies for Druid, go fast encroaching Vines or slower Trees (and Vines). Obviously there should be other more esoteric builds.
It must be so frustrating being "in the know" reading our alarmist musings and being unable to spoil out of turn (unless you are Arcanus, can we guess who that is?). I've decided to just have a bit of faith all will become clear in time (Although I'm worried about current inability to leverage Poison Immunity with Plants not seeming to be hurt by the more obvious direct damage effects). So after "jumping the gun" with my worries, I think I will just analyse each new card, consider its ramifications on current builds as well as new set interactions, and wait for the climax when we finally get to see the whole set. And it couldn't come sooner.