Complexity means "many parts in intricate arrangement" by removing birth signs and classes it makes it less complex by definition, no? Whether or not this is a case were it was a good decision is yet to be seen, I prefer to expect the worse that way I won't be disappointed.
What you choose in the character creation menu isn't all that goes into creating a character. The loss of classes is really no less complex because we have all the same skills (well, 18 of them). Just because you choose some as a Major skill doesn't add complexity. You will still limit yourself (or not limit yourself as the old system also allowed) as you play the game. The loss of birthsigns is a direct loss. However, the addition of perks more than makes up for it. Perks are going to make character creation and development much more complex, even if they all svck. More variety, more options. "Many perks in intricate arrangement".
I know what has been confirmed to not be in the game, and I'd like to know the reasoning behind it.
Okay.
Less weapon types: What do you mean by this? We still have all the weapon types Oblivion had. We may even have more variety in the weapon types, from what we've seen. 13 ores for Smithing probably means 13 weapon materials. Oblivion had 8.
Armor slots: We can only speculate of course, but I imagine it was to eliminate clipping, either what comes naturally from the detail they're adding to armor, or from options added in Smithing.
No spellmaking: Caused by the complexity of the new spells. Spells are not just the same projectiles with different skins now. Lightning bolts and fireballs are different things. Additionally, each spell can apparently be cast in different ways, which would be pretty hard for spellmaking to duplicate. In general they're going a different direction with magic, one that does not lend itself well to spellmaking.