If we go for maximum rule of cool and ignore all the impracticality in giving him a humongous longsword, one can argue it will be safer because his attacks have more range, and he can always drop it and fight at close combat.
If we're operating out of some bizarre artificial hypothetical where for some reason he absolutely needs to be on a battlefield and can't be replaced by literally anyone else for some reason, and also this scenario where it's super important for Wolf to be fighting, for some reason Mathilde doesn't need her sword, and we're prioritizing safety by way of range instead of safety by way of him not being on the battlefield in the first case, he's a dog, why is he on a battlefield, then it would still be better to give him a gun or a crossbow or a bound spell or something, which would very easily outrange a sword and be a lot easier to rig up for Wolf to use and would leave Wolf's mouth free to bite if necessary.
And let's just do away with the core pivotal assumption that rule of cool even applies here in the first place by saying no the fuck it doesn't. You don't just say oh wolf cool sword cool wolf plus sword equals two cool, there's more to creativity than just going down a checklist of preapproved concepts. It might be cool if Wolf was some sort of warrior dog and this was an expansion of his killing ability and him surpassing the abilities of his form, but he's extremely not! It's been very important to the characterization of Mathilde that Wolf is not a murderbeast, he's a companion! He's friendly, he's nice, he likes playing games and making people happy! He's an expression of Mathilde's inner joy and positivity and optimism and desire to believe the best of others that still lives on despite her hefty responsibilities and often grim work! Him taking up a sword would be a tragedy, it would be a symbolic abandonment of Mathilde being able to balance her responsibilities with her personal happiness!