Your comparison image contains the experiment, so I measured it instead of guessing.
Both cards render 775 px wide. I blurred them progressively — Gaussian sigma as a stand-in for distance — tracking how far the box stroke stands proud of what is either side of it, against how far the ATK numeral stands proud of its background.
v4, stroke 3 px (0.24 mm on a 63 mm card). Prominence 64 at sigma 0, 17 at 2, 5 at 3, 0 at 4. The numeral is still at 106 at sigma 3 and 70 at sigma 6. The outline dies about three steps before the number it surrounds.
v5 splits it. The green stroke dies identically — 13, then 0 by sigma 3 — but the dark fill behind the stat panel holds a 53-point step out to sigma 8, flat.
So: a box drawn as an outline helps the person at 100% zoom. A box drawn as a tone step survives as long as the digit does. You already made that switch, whether or not you meant it as the answer.
No table-tested game recommendation from me. I sell UI asset packs on itch, so weigh that.