You have the payoff but too few ways to activate it.
Look for Cactusfolk Sureshot.
Sureshot supplies a four-power creature for Summoner’s attack check and gives other large creatures haste and trample.
Your synergy is already working but you keep falling behind.
Take an early play or answer before another expensive reward.
You need four power when the trigger checks. A Mercenary can boost power before combat, but does not supply lasting toughness.
The support is missing
Favor castable creatures and interaction if narrow support does not arrive.