+1 to all stats really isn't as big a thing as all that, I find. The net effect is often just to raise one secondary stat from a 10 to a 12. It won't affect primaries, compared to a race that is a good fit for a particular class - such as for example a mountain dwarf fighter.
This is because raising a stat from a 9-10, or from 11-12 only costs one stat point anyway, but raising them at high stats costs double. So if the mountain dwarf starts with 14s in strength and con, he only pays 14 points to get his 2 stats at 16. He has plenty more to splash around. A dwarf fighter might end up something like: S16, D8, C16, I12, W14, Ch10 - or he could start with S17 if planning on going for heavy armour master at level 4. A human has to pay 18 points for his 2 16s so, while he gets more points to splash around, he is starting from a 4 point defecit when buying stats. A human fighter with +1 to all stats ends up something like S16, D9, C16, I12, W14, Ch10. So the difference is... Dex 9 instead of 8.
To be fair, where humans come out well is if you want a lot of 14s. So if what you want is a good all-rounder with no weak abilities then a human works pretty well... Just not incredibly well. You'e probably talking about 2 stats being 14s, but in exchange for not having a secondary stat as a 16.
However feats do change things, a lot. You can make a human archer with starting dex 16 and sharpshooter, or a melee guy who begins with S16 and heavy armour master. Feats that boost stats are seriously nice as first-level buys for humans because they actually give them the potential for a stat of 17, or more likely mean you only have to "buy" your way to 14 strength before adding +1 racial bonus and +1 for the feat. Crucially, you've got your feat and your primary stat at +3, so you can keep at the best possible pluses to hit and damage.
I'm looking at making a human paladin of Ilmater and heavy armour master seems perfect for someone who is used to taking punishment. I can have starting stats of S16, D8, C14, I10, W10, Ch16 and begin with the feat. I think that's really quite good, both as a very useful ability in-game and as a characterful thing that will make my paladin different from other ones. Compared to the human with +1 to all stats it only loses out by making a 12 into a 10 somewhere. A mountain dwarf, dragonborn or half-orc paladin could start with S17 and take the feat at level 4, so they'd still be at the best possible hit and damage modifiers as well, but I think the feat is at its most useful at low level.
The advantage is arguably even bigger for humans with feats that don't give any stats. You get to start a bladelock with warcaster, or an archer with sharpshooter, and still have your primary stat at 16. Anyone else who takes the feat at level 4 falls behind you on their +to hit and damage. They catch up at level 12, but that's waaaay down the line, and you've been able to play with the feat for all that time.
The extra skill is also really handy, and all the more so because it's not linked to your class or background. So you can give your paladin perception or your druid stealth, or whatever.
Overall I think the feat option marks a tipping point as to whether humans are the least powerful race, or the most powerful. That does depend quite a bit on the class you're picking and the feats though. A wizard or cleric probably wouldn't be changed all that much by a feat, so you might be better off with one of the races that gives you other interesting benefits.
Everyone suffers by taking the standard array instead of buying stats - apart from the half elf and a variant-rule human. It gives you a 15, 14 and 13 and you kind of need to boost both the 15 and 13. That makes it impossible to start with 2 16s and a 14, though you can have a 16 and two 14s or two 16s and a 13 - which you'd never do with points buy. My variant rule paladin would probably end up with wisdom raised to 12 but cha reduced to 14. That wouldn't be too bad.
