This is exactly my own problem with the martial power source, i.e. emphasis on "cinematic stunts" that I just cannot wrap my mind around -- I *could* call them special "techniques" empowered by Chi/Ki, but that doesn't work for a "typical" D&D character in a pseudo-medieval setting ("How does my 1st level farmboy-turned-adventurer know how to pull off these stunts, if it would take years of martial arts practise in RL?"). It's not just about 'Split the Tree' -- I couldn't imagine how it works when a rogue uses, say, 'Blinding Barrage' on a group of Ghosts or Golems, or when a ranger uses 'Hammer Shot' on the same creatures.
Why not? as far as I can tell from talking to martial artists every one has ki and in principle can tap into it. Normally people do but in minor ways. No for every 1000 farm boys/street urchins that need to do Blinding Barrage only one manages it and lives to tell the tale. That is enough for me at least.
After all, how is this stuff idscovered in the first place. Monks do not discover matrial techniques in the monastery (back when they started out) they found the need to do it in battle and if they survived and because they are so in tune with their bodies they stumbled on ki and by study and excersise they leaned to exploit it and teach others how to do so.
That does not stop others doing so either but lacking the Monks training and body awareness and medtiative techniques they will never pass on that learning.
Does that work better?