Ok couple things, it's dirt cheap to get this running. Literally ten spell points gets you 6 birds and two Rajan Furies. That gives you 110 more points to go with "some other crap in case this doesn't work." Yes you can counter the aviary but those counters won't also work on a buffed up mage or some solid big guys(bears don't care that you have a damage barrier they've got....well bear.)
The single greatest strength of the Straywood Beast Master is his versatility and ability to build books that adapt very easily. High Armor? You've got Rhino Hide, Gator Toughness, Wychwood Ironvine, Animal Kinships and the only Acid resistant chest piece in the game all in school. Beat down? You've got Bear Strength, Wolf Fury and again Animal Kinships all in school. Range game? You've got two good range quick actions with Hawkeye in school. Cheap tricks used by Biblofilter? Straywood INVENTED the ole Force Push em through a Wall of Thorns game. Nature does passive healing better than any other school and while a Beast Master is NOT a Druid on that level they still Have Regrowth, Regrowth Belt, Wychwood Ironvine, Etherian Life Tree, Mohktari Great Tree of Life, Iguana Regrowth, Bulls Endurance, and Gator Toughness all in school to heal/extend their lives.
While Beast Masters might not be THE best at anything(and I'd argue they still swarm better than anyone) they're at least SECOND best at a host of things.