Strategic depth isn't actually about what has more numbers behind it, its what asks the player to be more versatile and intelligent.
The happiness in Civ IV did not have a significant impact on people's playstyle, therefore it didn't add very much depth to the game. Civics aren't permanent, I don't have to consider much beyond 30 turns ahead when I choose a civic because I can always switch back. Social Policies require longterm planning, and it forces you to consider way more factors. Religion really was a paperthin element, and it basically translated to "I can have +2 with this guy, or +2 with this guy, well, it doesn't really matter because I can switch any time."
Once again, more choices/ descisions do not always relate to as strategic/difficult/intelligent choices. The idea that because Civ IV had more numbers behind it makes it a more strategic, complex game just deosn't stand up to scrutiny.
I agree, complexity has nothing to do with the numbers, both games are full of numbers, whether you can see them or not, they're there. I never said more numbers mean more complex, in fact I only mention numbers in an example that compares game mechanics in both game that happen to both use numbers.
Yes, you can switch in and out of civics but like I said you have to weigh the benefits to the cost and it does cost you something every single time. SP's are a one time thing, it's a buff. Yes, you have to make a choice on how you are going to play this particular game but once it's made that's it. Where's the versatility in that?
Yes, religion is as you say but again you have to choice who you want that +2 with and weigh the consequences of losing the +2 with the other guy. A choice as simple as that could mean war in some situations which is huge.
Once again, I'll agree that more choices doesn't necessarily mean more complex. But more choices that effect actually game play absolutely means more complex. The numbers have nothing to do with it.