I originally read the buff as being weaker for airborne creatures. Your intention makes this synergize too well with itself
I agree... An interesting remix would be to have it give airbornes -3|-0... That would also make web a bit more versatile and help wings users out as well.
I.e if used on a grounded creature, it gets flying and gains attack.
If used on a flyer, it looses attack.
Then you would have to mix in spiders if you want to be able to repeatedly buff things, but even without them, it would be a very useful both defensively and offensively.