“In family law cases, pleadings should only be struck, and trial participation denied, in exceptional circumstances and where no other remedy would suffice: Purcaru v. Purcaru, 2010 ONCA 92, 75 R.F.L. (6th) 33 (Ont. C.A.), at para. 47. The exceptional nature of this remedy is rooted in the significance of the adversarial system, as this court recognized in Purcaru, at para. 49.”