Not agreeing here. With 4e, the difference between someone with proficiency and someone without is 5 (plus whatever difference in stats, assuming the same level). With 5e, the difference between someone with proficiency and someone without (omitting roguish expertise) ranges from 2 to 6 (plus whatever difference in stats, assuming the same level). So for most of a PC's career, the difference between skilled and unskilled is less than in 4e, and it's only greater than for a handful of levels many campaigns never get to.
Moreover, since most monsters don't have a lot in the way of proficient skills, they aren't leaving most PC skill bonuses in the dust even if non-proficient. And this is true no matter what the level vs level comparison of the monsters
It ranges from 3 to 18, actually, depending on the details.
A Paladin in plate armor has little need for Dex, and several stats that need to be high (Str, Con, Cha, arguably Wis). Dex is a plausible dump stat. Same for a Str Fighter who wants to literally anything other than
just fighting. A Barbarian has no need for Wis, etc. Hence, the floor is not +0, it is -1.
That -1 will get worse and worse relative to the creatures you oppose. People who are truly great at a stat will have Expertise and their main stat supporting it, which maxes out at 5+6×2= +17. Hence, the maximum gap is +18 (counting a dump stat's -1). Even for ordinary efforts, without Expertise, the gap is -12.
All characters in 4e get half level bonus and every stat increases by 2 (meaning, modifier +1) by the time you hit Epic. The natural gap (barring feats and the like) will essentially never be greater than 14 points, counting both stats and Training. Since folk make such a big deal of 5e being "4e math ÷ 2," that means the gap in 5e should never be greater than 7. Since this is demonstrably not true (and, in fact, the maximum gap is almost twice as big!), I stand by my statement.
In 5e, everyone slowly falls behind on anything they aren't investing in. Especially saving throws, a known weakness and common complaint from early 5e. In 4e, everyone does get better, even at things that aren't their focus. A 5e "clanker" Paladin will
never be any better at sneaking past a level 1 goblin than they were at level 1 themselves, unless they waste valuable resources on doing that alone. A 4e "clanker" Paladin actually does learn some things about being sneaky, and can sneak past that level 1 guard much more easily (but, notably,
not necessarily guaranteed; even going from a -1 to a +15 is unlikely to ensure victory in all cases!)