Exactly, the context is completely different. The math and abilities set up of 5e is very different from 1e where stats mattered much more.
To be fair - and I certainly would like to be fair - a three-point difference in, say, DEX, in 5e matters to the tune of +1 or +2 to your AC, depending on the even/odd split, while, in 1e, how much a 3-point difference matters to your AC depends on what it was to begin with. Between a 9 and a 12? Not at all. Between 14 & 17? Three full points.
I'm not sure how that's "mattered more." High stats were more important than middle-of-the-road stats? I mean, if you're rolling 4d6 and got 16,16,14,13,12,9 vs 16,16,10,10,10,10 in 1e, there's not a big difference, but in 5e there is; conversely rolling 18(00),17,15,13,11,9 vs 17,16,14,12,12,12 is a huge difference in 1e, while a fairly minor one in 5e. Doesn't seem like a terribly important point. They're a bit different, sure.
I think "less consistent" might capture that difference more accurately...
Edit: ... oh, there's another sense of stats 'mattering more' that's coming up more often. For instance, if you were trying to recruit henchmen, your CHA mattered in 1e, including otherwise minor differences between a 9 and a 12, for instance. OTOH, if you were trying to do almost anything else, it didn't. If you weren't a Magic-User, INT only mattered for the number of languages you spoke. If you weren't a cleric, your WIS really didn't count for much, etc...
In 5e, every stat has saves and other checks that use it, so it seems like stats matter plenty.
I'll take that bet! The rest of the stat block is only possible with an 18 Dex. He's a level 10 Thief with an AC of 2. You need a minimum Dex of 9 to be a Thief, and he only has +1 Leather and a Ring of Protection +1 to adjust his AC. In order to get an AC of 2 with what's written in his stat box he needs an 18 Dex.
Well, then, he must be a master of disguise!
(No, wait, in 1e only Assassins - OK, and Illusionists, sorta - could be masters of disguise...)