He does have a point there. But he doesn't seem to touch the criticism about over-balancing he gets, where his tunings often make everything feel flat and samey since all's finetuned to such lengths that it doesn't feel like much of anything; and to which he himself is probably blind to due to having played with numbers so much (e.g. seeing a big effective difference in math that's more or less irrelevant in all practical ways to a normal eye that doesn't immediately overthink it and calculate what it might mean if it's ten or twentyfold).
The question is what you mean by "flat".
Is it "+15% looks too boring, why can't it be +3 instead"?
Or is it "Why is this all just numbers? I want an ability that gives my character an extra arm that can wield its own weapon while turning 1d4 enemies into chickens."
IMO, the absence of things like the latter is fundamentally a content production issue rather than a balance issue.
I don't want to speak for the other posters, but I took it to mean that various items feel ultimately very similar.
I forget the exact numbers, and maybe this has changed with the updates to POE, but for example a sword might have x damage, y speed/recovery, z interrupt or whatever and do slash and pierce damage (picking whichever is more effective against the targets armor).
Now take some other 1h weapon and it would be balanced so it's basically roughly the same damage output as the sword (almost always), by doing x-25% dmg, but at a speed which offsets this, and the interrupt is shortened by exactly the amount needed to be basically be the same amount of interrupt time over 10 seconds or whatever as the sword (which attacks slower but has longer interrupt) actually has.
The damage type might be only slash for this second weapon, so some armors are more effective against it, but the weapon will likely have some other special thing to somewhat negate that. In the first place damage type is fairly unimportant as you can switch weapons quickly enough before hitting enemy lines, and any other advantage is mostly not that big so it matters little (like the armor negation... Ok, it's mathematically better than the other advantages in most cases, but it's so little esp vs. path of the damned resistances that it doesn't really matter all that much either).
Armor is similar in a way... More armor means less DPS because your recovery becomes slower and slower. The damage resistance theoretically makes up for that, at least against basic enemies (esp. single enemies, not so much groups maybe)...
The spells are different in this regard as many are mostly trash (esp. considering their often limited amount of uses). But like you said in a post below, the fact that you can miss most spells easy doesn't help. People then go low-risk and use whatever does the damage most reliably or bucks the RNG in some way.
Originally accuracy was also just based on class and levelups, not something you could influence with stat increases outside of weapon enchantments and such. That meant that most classes would end up being way too predetermined in terms of what you could actually do with them.
At the end of the day it's all rather... Flat. In one class of items (like 1h weapons, or at least 1h weapons of a certain size) the differences are... Well, it doesn't really matter that much what you use or when (mostly). There's nothing that really feels all that unique about the various weapon types. It's all "pick one, it mostly doesn't matter".
Any exceptions to this were patched out while I was still playing the game. Any strong build was usually nerfed as well usually.
It's this philosophy that reminds me a bit of Dragon Age 2 or various MMO's and such...
"Ok, you can fight with a greatsword, twin daggers, or a bow. The greatsword is slow and high damage, the daggers very fast and low damage and the bow medium damage and slow speed, but shoots at distance". I.e. it all works out more or less the same.
If the weapons and armors in POE had gotten a more realism-based treatment (in terms of what they are used for, what movesets they have, what special attacks and so on, how well they penetrate various armors, point control as +acc etc for weapons, renaissance based full or three quarters plate armors being largely arquebus, crossbow and bow proof) I think this would have made the game much more interesting. Daggers should not be primaries for example, but secondary/tertiary weapons for when people are grappling or something, or when you are in social setting sout of armor... Halberds and such should be primaries against larger beasts, and to hook and make plate armored guys (and others) fall to expose weak spots or bind their weapon arm temporarily. It'd require Sawyer to not just talk about history though, but actually think about how to make it matter in terms of mechanics.
You could add however much complexity you want, and it would likely not feel flat like Sawyer's systems. Your landsknecht doppelsöldner greatswordsman type in full 1600's plate could charge through enemy ranged attacks and bind pikes with his weapon, while your own pike guys come in right behind to attack the enemy line... Halberdiers could try to counter greatswordsmen. Guys in full plate could have the downside of overheating with too much fighting if your own guys can't help them take out the enemy in time. They'd have to raise their visor (or lower their buffe) or open the little window in the most advanced close helmets to breathe, making them vulnerable to pikes and ranged attacks etc.
Greatswords wouldn't be great vs. enemy plate armored dudes, lacking easy ways to hook or attack enemy weakspots.
Or it could be simpler, whatever.
A dragon could be kept at bay somewhat with pikes/halberds, his breath/spells by wizards counterspells or paladin/priest auras, while 1-2 flank it to harm it's legs and tail to immobilize it or whatnot, or cast acid spells at it, or while some militiamen from the nearby town who you talked into helping you or who gave you the quest to kill the thing set up a ballista to kill the dragon with while it's distracted by you and not dodging.
This would make large monster fights make more sense... Rather than your tanks running in and just... Taking hit after hit from a dragon while everyone else just slowly reduces it's bloated HP pool.
Point is there is a lot that's possible to help make the combat feel new and interesting, make players find new tactics compared to the stuff you had in the past. You can have weapons feel very different from each other, each having multiple specific roles it's good at while being somewhat awkward or even bad in other situations instead of everything being too similar and samey.
