Well.. with the prevalence of Talonflame, (Mega)Blaziken & the Mega-Charizards in the new meta, Leavanny is basically useless. It's gained a niche as a Sticky Web set up while holding sash, but even then, Galvantula is better because it only has 2 weaknesses and an amazing ability that lets it fire off Thunder without rain. I don't know what kind of battles you fought, but a fire type not carrying a fire move is really uncommon. Even bulky fire sets usually sport Lava Plume in order for a burn chance.
Leavanny has very circumstantial abilities, sparse movepool, no coverage moves, no access to any status moves that induce sleep to help it set up, mediocre stats and very poor typing.
Even if you needed a water/ground counter, you would use something with better typing/ more useful moves/ abilities, e.g. (Mega)Venusaur/ Tangrowth/ Amoongus/ Trevenant/ Gourgeist/ etc., that could do more for your team than just counter a water/ ground/ grass types.
As for Bug typing resistances, I take your point. I guess it's a bug eat bug world out there.