You keep acting like this is some kind of new, additional burden being placed upon you. You had six stats and AC from the very beginning. In fact, you originally had five saving throw categories as well.
3E reduced that number - you now had your six stats, your AC (and some variants) and your three saves.
In 4E you had six stats, AC, and three "defenses".
Now you just have six stats and AC.
Why is this somehow adding complexity?
It adds some degree of play-time complexity because there are more things an attack can target. The six ability scores in 3.X and 4E are used to calculate saves/defenses, then can essentially be ignored for routine attacks/spells. It does reduce character creation and leveling complexity, but those are relatively infrequent events compared to being targeted by attacks/spells. Essentially, it simplifies a rare event at the expense of a common event.
Is it a big deal? Probably not. But consider that it's less likely that a player will successfully memorize 7 defenses than 4 (especially if they're also trying to remember their attack and damage bonuses). Fewer lookups on the sheet means faster play.