Sticker-less cubes fall into the same category in my opinion. I mean, you can see more stickers, but will you really use it to your advantage? I think that if you can see more of the cube than another person, then it shouldn't be allowed. Even if 99% of people won't try to cheat/use it to their advantage, you will always get those few people, who try to get an unfair advantage.
I think pillowed cubes should be competition-illegal, except for the 7x7, which, I'm kind of neutral on, and wouldn't wind if the pillowed version went competition-illegal, or stayed like how it is now. All rules are there for a reason, and if (like you claim) pillowed cubes except 7x7 are illegal, and sticker-less cubes are illegal, then they shall remain illegal. Even if there is only a slight chance of it being benefited from, it will still eventually be exploited.