...sure, you "write your own CAS in python".
More seriously though, while constructive criticism is great and often can be very useful, your approach to with statements like "Whoever made it has disgraced his own family" is over the top, and maybe unnecessary. But I suppose your post has gotten a lot of attention, which perhaps was your ultimate goal.
Having said this, your core criticism is valid, I believe. 2D input has indeed been a major failure on many fronts. Since its introduction (15 years ago now!) it has been a constant source of frustration for many users. After all this time, it is still buggy. There are countless posts on mapleprimes related to problems with it, where the proposed solution is essentially to switch to 1D input. All the top commenters here seem to use 1D input as far as I can tell, and for many maple users the first thing to do after a new version installation is to make 1D input with the worksheet interface, the default. I've been in university courses where maple was used, and the instructors gave actual warnings to new users to *not* use the 2D input (that in itself is almost ironic given the very point of it in the first place was to make entering math simple for students).
1D input, will surely relieve at least some of your frustration. It is superb to use (as far as entering the math goes, and copy/pasting to outside editors for example - it's simple ascii after all!), and has some nice benefits over mathematica (for example: use of single underscores is allowed in variable names, double underscores are nicely parsed in output as subscripted variables, eg: alpha__a).
I actually also agree with you that the user interface design (or alternatively the flexibility to configure one the way one wishes) is really very important in the enjoyment one gets from using a particular tool. Here, even with 1D input, maple suffers a lot. Perhaps, due to the resources being consumed polishing the 2D input and the document interface, the 1D worksheet has not changed much (for "power users" anyway) during the years. Basic things like syntax highlighting, or keys configurability (i.e. basic key bindings to move forward/backward a word/character, etc) are still not there (!!). This is stuff that virtually any text editor has. When one compares this to modern interfaces like juputer notebooks (where one can for example use vim bindings!), or sage notebooks, it's difficult to argue that using maple is not a pain, even in 1d worksheet mode. These days, when possible, I also find myself choosing to do stuff in python, etc, simply because of its much better user interface (i.e i don't have to reach for the mouse ever 1.7 seconds).
This has somehow now also turned into a whining post I suppose... so to finish, let me change tones a little and point out that even with all these shortcomings mainly related to the poor interface, for many of my use cases (essentially manipulating/simplifying/approximating large sets of equations) maple is still absolutely untouchable. It's capabilities as CAS (in my use cases) are just not matched by much else out there... and I guess in the end that probably matters most.