How much effort does it take for a theme development?

We have a team WordPress developers, supposing that we all have hml of shortcode, elements & animation, interaction; We still take around totally 600hours effort in WordPress development/implementation/demo/for a general business theme.
I did a search on old forums and someone say they can finish within 1-2 weeks. is that possible?
We use Redux Framework and did develop a core by our own but it just reduce 25% of the total effort and everyone think that this is the minimum.
However, I can see that we are working very slow but I don’t know or guess how slow in comparison to the others to push all of us move faster.
How much total effort do you guys take for a common theme?
Hope the forum is a good place to share experience and the senior authors can help all of us (newbie author) or share the method to do it faster.

The time required to make a theme has been quickly escalating. I think the two weeks development time you read on the old forum was from years ago.

Even with a team it may take at up to 2 months to make a theme that is acceptable on this marketplace. The reason for this is due to the sharp increase in quality standards and the rise of the mega themes.

If you make a simple niche theme, it will need to either be picture perfect or have some really compelling features. Which I turn increases development time.

2 week time is enough for an expert team with decent number of members. But one gets rejections and wait in queue. So normally it take 2 to 3 moths i guess.