Shaper hits the board, and once, only once, on the FOLLOWING TURN it activates. so the opponent has a turn to react before the burst.
Also, regarding the "just make 24 pillars and 6 shapers" that deck would not be great. assuming 7 pillars and a shaper opening hand:
Turn 1: 3 damage (97 hp)
Turn 2: draw pillar, 9x3 = 27 damage (70 hp)
Turn 3: draw shaper, 6 damage (64 hp)
Turn 4: draw pillar, 11x3 = 33 damage (31 hp)
Turn 5: draw shaper, 9 damage (22 hp)
Turn 6: Lethal
That's fully upgraded for 6 ttw with a pretty much perfect draw, and not getting hit once by CC. Definitely not OP.