The thing is, Wahl's magic isn't particle nullification or something /that/ profound. It's plain old Weakness Magic.
Wahl isn't only a bad match up for Laxus; he's pretty much a bad match-up for everyone fighting him solo. You can see it right here:
http://www.mangapanda.com/fairy-tail/459/15
Wahl pretty much reveals that he can exploit weaknesses in people and in their attacks. Juvia sizzles against a steambot, Gray's Wahlbot spews out flames, Lisanna faces a steel tank, and Elfman is pitted against a speedster. Wahl is a perfect counter to EVERYBODY, whatever their abilities may be.
In Laxus's case, what Wahl needed to counter and exploit was the rune magic that Laxus set up.
How do you get rid of runes? Either you rewrite them or simply fulfill the condition needed to dispel them. In Laxus's case, the condition was to cancel the MBPs.
Poof, Wahl counters the runes at the cost of cancelling the MBPs and ultimately healing Laxus. It was that simple, tbh. Dunno why people tend to overthink this.