I misspoke, it's level 8, which is like level 15, not level 7, when half-proficiency gets to +4. IME, most characters get to at least 18 in their primary stat by level 8. Sometimes that's by starting with 17 and taking a half-feat somewhere, so I guess that option is still open.
Casters rarely have more than one feat that is a higher priority than boosting their spell DC (and builds that do are likely to go variant human)... Monks and Paladins have two stats to invest in, so they really want some ASIs. And fighters normally have five ASIs before level 15; they're almost certain to have 20 in their primary by then.
But again, you have to remember this is
why I increased proficiency, so ability scores didn't have to be boosted for your character to still be enjoyable to play. You might play a Wizard with a INT 16 at 1st level. By 4th level, you could have an INT 18. At 8th level, with the +7 prof bonus, you are +11, the same maximum you could have in 5E. Even if you never boosted INT via feats, at 10th level with +8, you are also +11 total; no different from the +5/+6 combo of ability/prof in 5E.
Sure, MAD characters might not have single scores as good as SAD, but they have better scores elsewhere. Again, I never expect a MAD character to have 16's or higher in three scores. You can do it, it isn't even that hard to get two, which IME is all that is normally
really needed for most MAD builds. The third score can be a 14 and still work very well.
Allowing players to place the +1 in any score if a feat grants one, makes it entirely possible, if a player really wants it, to still have a 20 by 6th ot 8th level in L10. But, if they do that, then obviously
that was their priority. Is it necessary though? Absolutely not, unlike in 5E is assumes you will use at least some ASIs to get an 18 or 20 in a prime ability score. Something, BTW, I never liked... so I removed that need.