The old hot dogs and buns problem (10 per pack vs 8 per) remains unresolved to this day as well....
All kidding aside, it never crossed my mind because I’ve never put cards of any kind in 9-pocket vinyl sleeve pages. I’ve never trusted them not to eventually bend or warp the cards, especially the super-flimsy tan-back stickers. But if I did use them, of course I’d vote for 9-card subsets instead of 10, no question. By similar logic, a 55-count base set is a bummer too because 54 would be an even multiple of 9 also.