I can't stop masturbating

>the tetrapod efficiency meme
Land vertebrate tetrapodism is basically coincidental - it's a consequence of:
a) The Sarcopterygii subgroup that evolved amphibiousness had only two paired locomotive fins usable for land movement.
b) The endoskeletal structures characteristic of Osteichthyes (of which Sarcopterygii are a part) are highly costly to grow and difficult to duplicate without disrupting vital systems given the layout of bony fish organs - basically, the evolutionary options are changes in size or limb loss; gain of legitimate limbs is STRONGLY selected against in tetrapods because it essentially requires major birth defects, and it has nothing to do with efficiency. 4 is usually enough not to "require" more, and evolution is more a game of what gets the job done than what gets the job done "best."
The best counterexample is of course arthropods - they evolved amphibiousness and terrestrial survivability independently of tetrapods, and number of limbs is highly variable in arthropods. Flighted insects are effectively ten-limbed by tetrapod standards, because of their two pairs of wings (elytra still count as wings).
A less commonly cited counterexample is mollusks (also evolved terrestrial survivability independently), where the truly land-dwelling mollusks have effectively one locomotive limb, and the tentacles are less like limbs and more like external tongues.
Even within Tetrapoda, there are legless reptiles, as well as species of reptiles and amphibians with two arms and no legs. I could easily see that arrangement leading to complex tool use.
One thing nobody talks about, though? Just how predicated the evolution of civilization-capable life on Earth was on the existence and surface abundance of trees