I also shoot my bows (all bow types) as if holding a tiny bird in my hand. After a few seconds the imaginary bird (usually a Grackle or something similar...don't much like those Grackles) looses consciousness, feathers still solidly intact but with zero room to wiggle, move up/down/sideways, flap around or twist. By the time the release is made the little avian creature is firmly sqeezened' into a nice reliable repeatable controllable possession in my hand. The bow feels solid and in control, and shoots/feels great. The imaginary bird isn't doing so well.
Kidding aside, there's a misnomer regarding what 'firm' means in regard to grip. It does NOT mean a white knuckle choke-it-like-a-boa constrictor hold, but rather secure it like you want to solidly control it, rather than letting it control you. Not talking about a light and balanced target bow in a target line situation here, but a hunting situation where bows of all types and designs and with all manner of add-on accessories are turned and tilted in all manner of shapes and angles. In this kind of shooting, regardless of the bow (but especially with low-mass bows) grips that allow a consistent and maintained line throughout the shot, establishing a solid UNMOVING line between the arrow point and drawing elbow until the arrow is away, will work. Guaranteed. The grip shape (longbow vs. recurve) has less to do with it than getting and MAINTAINING proper alignment. In hunting situations hunting bows that control you and move where they want to will shoot where they want to. Which might not be where YOU want to.
Think of it in terms of a shotgun, another recoil-oriented (vibration-oriented) hunting weapon often shot in less-than-perfect situations. Which works better, pulling the rearstock of that 12 guage snug to your shoulder before squeezing off with a slight hold on the forestock, or letting the entire weapon just sit like a bird in your hand, loose to do it's own thing, until the big kaboom happens?
Firm vs. loose, controlled vs. unfettered. It's all opinion for sure, and so it should be. As you can tell, I'm a believer in what H. Hill used to say and practice when shooting a bow. 'Get ahold of it'.