Gardy doesn't outspeed Grumpig, surprisingly, they are in the same speed tier. That doesn't make much of a difference though. For me, Grumpig covers my weaknesses very well. I like to run Coil Serperior and Grumpig takes care of both of his weaknesses. Grumpig has the bulk to take on even SE special attacks (shadow ball, signal beam). He also is faster than Lickilicky meaning he can twave or heal bell or whatever he wants to do at a faster rate than lickilicky. Most people see him and don't really know what to do (because lol nobody uses him). He's a great pair to offensive teams that need to set up as well as stall teams. I don't use stall much though, so I can't really place him on that.
Lickilicky also has a bad 4Moveslot syndrome that Grumpig doesn't. Grumpig has a good role and can work with it. Unfortunately, it is let down by having no reliable recovery aside from the obvious rest+leftovers (why doesn't it get recover? :[ ). Like I said about Charizard running around, Grumpy takes care of him no problem and can use tbolt if he really wants to KO him but that's not what I would usually do. Also, it takes the ever-increasing Piloswine. Een though Pilo has physical attacks, Grumpig can switch in on ice shard/icicle spear and outspeed and hit pilo with focus miss (what I use). So, yeah, it's reliable, but not on the same level as lickilicky, but is great if you want something that has a little bit of reliable attacking prowess.
Thank you for your time.