I often hunt in areas where shots could be close enough to leave powder burns on an animal. I use the same rifle that I'd use in an area where I'd expect 400 yard shots.
There is no such thing as being too close for optics to be a disadvantage over irons. Any scope with 2X or 3X on the low end of a variable is fine for 10 yard and under shots. If your scopes start at 4X you may be at somewhat of a disadvantage at shots inside 5-10 yards. Any scope is a huge advantage at seeing your target in poor light, far better than irons or dots and that is exactly when most shooting happens.
Any cartridge that is adequate at 400 yards is just as adequate at 4 yards, but the opposite is rarely true. I don't believe in the myth of the typical close range brush gun.
A typical lever action zeroed at 100 yards is still going to be 2-4" above or below the line of sight at ranges between 50-125 yards where almost all shots are taken. My Kimber 308 scoped is over a pound lighter than my levers in 30-30's, 35's and 44's are unscoped and the bullet is never more than 1/2" above or below the line of sight from 50-125 yards. That is how you shoot through OPENINGS in brush. There is no such thing as a round that can shoot THROUGH brush without being deflected.
The arched trajectory of typical brush rounds is less of a disadvantage on longer shots in the open. You can always hold high and drop rounds in out in the open and in good light. You can't do that in thick brush. This is where laser flat trajectory and pinpoint accuracy aid in putting bullets through small openings. Optics help you see twigs and limbs between you and the target so you know where to aim to avoid them.
The perfect brush gun is a lightweight, scoped bolt gun that shoots flat and hits hard. With a mid powered 2-7X or 3-9X scope it is versatile for any hunting situation from 4-400 yards. Mine are on the expensive end, but there are 6 lb options such as the new Ruger American, TC Venture, Tikka, and several Savages that are priced considerably less than lever guns.
My brush guns.
Winchester EW, McMillan Edge stock, Leupold 2.5-8X36 scope, 7 1/4 lbs.
Kimber 84M, Leupold 2.5-8X36 scope, 5 lbs 15oz.