This Play style involves a lot of damage. A Building Play Style will get overpowered by the extremely high damage, but, being only the Rocket, Baby Dragon and Valkyrie that are able to multi kill so a Swarmer Play Style will obliterate this play style quickly.
This Play style, having only buildings, might have a problem with troops that attack buildings only, because they do a lot of damage. You can substitute the Furnace with any of the spawners, but, the Fire Spirits are the projectiles so it does not technically have any troops. The only attackers are the X-Bow, Mortar and Furnace because they are the ones that actually can get in range of one of the Crown Towers so use them together.