Are you talking about racking the slide back with an empty magazine in the pistol, so that it will lock open? Or are you talking about pushing the slide back until you can press up on the slide stop, locking open the pistol? Both are manual procedures, but it's easier for me to rack the slide with an empty magazine in the gun so that it locks open, than it is for me to push the slide back with one hand and push up the slide stop with the other. For one thing, it takes more coordination to do the latter, which I don't have in abundance, and it's harder to hold the gun and move up the slide stop while pushing the slide back until it's in the right position.
It's been a while since I've had a Glock or a Shield 9mm, so I can't really compare them from memory, but the RSA on my Shield 45 seems much more "stout" to manipulate than on my Ruger SR1911 CMD. I guess they have to be on the smaller, shorter guns to overcome the inertia of the slide's rearward movement under recoil, etc.
If your Shield is operating and ejecting reliably, I'd say it was normal. You don't want too light a recoil spring, or it will end up damaging your pistol. Too heavy and you'll have performance issues.
Maybe you just need to shoot it some more, for it to lighten up a bit.