It's not useful to try and debate that one field is more difficult than others. All three fields employ a mix of people with varying intellect. It's also not useful to make silly claims that every decent engineer you know had the intellect to complete medical/law school, or that numerous doctors/lawyers couldn't handle math/CS courses. Unless you're giving aptitude tests to your lawyers and doctors, which I assume you aren't. These claims are highly speculative and sound petty.
Your other comments are more worthy of further thought.
I don't understand why you feel software professionals aren't given respect. Nearly every "Best job" survey on the internet will list it #1 or 2, with several other technical jobs in the top 10. That doesn't necessarily equal respect, but the industry is certainly getting tons of attention and many are trying to enter through any means possible. I'm not sure how we can measure respect or disrespect, but I don't see it.
I know plenty of engineers that are making a good living with plenty of work/life balance that are well beyond 40. I'm sure there are some that aren't as well, but engineers that are mindful of marketability can have a long run in the industry.