Ok, but even in your scenario (assuming a Harmonized Samara Tree) you'd still need to wait 4 turns in order to get the full 3 mana (4 mana off the price of whatever you cast -1 for the mana you spent when Samara Tree casted the pod in the first place). Even then that's only 1 more mana saved than if you had casted it from the Vine Tree and you don't need to wait 4 turns for it then. Now I get that there's probably something I'm missing here, but what is it? Perhaps I'm underestimating the Seedling Pods.
Yes in a one round comparison vine tree will generally be > Samara.
Extrapolate that into a game wide effect and it can look something like this.
Druid cast a Samara tree.
Next turn Samara tree casts a seed pod A.
Next turn Samara casts pod B. A is at 1.
Next turn Samara casts pod C. Pod A is at 2, pod B is at 1 mana.
Next turn Pod A becomes anything you want it to be, Samara tree remakes pod A, Pod B is at 2, Pod C is at 1.
This cycle never ends. The Samara tree lets you spend 2 mana to get 3 in a few rounds, and that 3 mana is 100% versatile.
Also one of the biggest things to note here is that all of those pods, and subsequent actions, are a byproduct of the tree. The druid spent ZERO actions to make the pods. The only action was placing the tree. Free mana and free actions. I know Vine tree is more appealing but Samara has always been my favorite tree in this set. The sleeper hit IMO.
So what do you do? Rush in to beat down the samara tree? That is a lot of mana and investment for a turn 1 decision. Kill the pods? Well they have cantrip so have fun. I can spend 2 mana to make you waste an action or two killing pods that come back next turn. An Etherian Life tree, which a pod can become, makes them all 7 health to boot.
Pods not popping fast enough? Use a shift enchantment wand
Is she impossible to beat? Absolutely not. She is a lot of fun to play and very satisfying to beat.
However the Samara tree and/or pods are not auto include in her book, it is an optional route to go. You can focus on vines and all that as well; purely based on your play / book style