So, I believe that the easiest (fewest upper division classes we need to take) major in math department is mathematics. And I wonder if majoring in math and minoring comsc is easier than math/comsc in math department. Is that true?
I can’t help but feel like this way of thinking is counter to the point of you going to college/getting an education. Pick the major that interests you the most and select courses based on their application toward your eventual goal. If you want to do software take additional courses in software engineering even if they aren’t degree requirements because they will help you in your eventual career. If you want to do more math take modelling or analysis or what have you even if it takes an extra quarter to pass them. If you take the path of least resistance you’re wasting time you could have spent preparing for the future. I’m sorry if this answer is unsatisfactory because I didn’t directly answer your question. Good luck with your studies!
I agree with @Throwaway182 ,
All math majors I know will be in a hurry to jump to Graduate level courses, taking the necessary summer work to begin in the fall. Most likely, if accepted, will petition to replace math 100ABC w/ math 200ABC. Point here is that your are SERIOUSLY, throwing yourself away by finding a shortcut to graduation. (no pun intended ^^) In fact, you’d be in the same boat of those who think college is a scam because you can’t get employed right away… I remember reading an article about someone with a Ph.D working at Mcdonalds. Dont be that guy crying at the world!! (Apologies to those few who “legitimately” fall in the cracks of society)
In other words, don’t play yourself! Go the distance like Ali! 
You’ll thank yourself later in that job interview when you see 20 other people, all with a degree.