Hello,
Your opinions is correct from my side, I also seen that all themes have common contents and features that always return:
Menus
Footer
Header
Theme options (colors, logos, socials…)
Components (testimonials, images gallery, lightbox)
Blogs
Due every day the software of all web included Wordpress themes become more big, complex and good. The work behind them become every time more big. This is why there is a contstant research for do more by write less code, this is the only way for write bigger software in the same amount of time.
I’m the authors of Y | The Theme: http://wordpress.framework-y.com/, this is a framework for develop Wordpress themes that will be available for sales on Themeforest within some week, if you are interested we can discuss for a collaboration that allow you to develop a Wordpress theme with this framework and sell on Themeforest. I not allow this for others authors and I will not allow in near future. Currently I want try with only 1-2 authors.
Using a framework like this will save you 80% of work and you will be able to focus only on design and custom features. I already used this for 3 HTML templates that you can see on my TF portfolio. My last work is http://templates.framework-y.com/material/demo-main/ and required 20 days for the HTML version + 10 days for Wordpress version.
If you are interested contact me at fede@pixor.it
Cheers 
Federico Schiocchet