Hasn't Laxus demonstrated considerable melee combat abilities before? Also, I'd assume he has it, but there's the Fairy Law argument? He may also have some edge via his pseudo-flight even if he has to turn into Lightning against a Lightningrod user to do so.
Also, excluding Overgrow -which isn't its ability as Mega Sceptile; Lightning Rod is, hence the electricity immunity in the first place; But this may be a non-issue if Sceptile also has its non-mega abilities here also- & the Sp. Atk boost from Lightning Rod Sceptile doesn't have much statistics amplification of note here.
Admittedly, getting your Grass moves' power amped when in danger is great, as is the boost to AP for many of its attacks from Lightning Rod.
But Agility & Unburden don't matter that much, since, if my memory serves, speed changing doesn't work in Speed Equalized matches. Correct me if I'm wrong. Screech is sound-based, which Laxus may be able to dodge, & Leer may be of questionable utility.
Still, what AP boosts Sceptile does have give it an edge, & it'll be hard for Laxus to fight it, even in close combat, without his electricity. The life draining & Detect could also certainly help it last longer.
Other than Fairy Law, possible tactical use of Thought Projection magic, pseudo-flight, MAYBE the intangibility via Lightning Body, & POSSIBLY an edge in melee combat, I'm doubtful Laxus can handle Mega Sceptile.