no i havent.
i just unpacked the system.new.dat out of curiosity to see whats inside and found a lot of junk (not only in the apps,priv-apps,meizu apps folder) so propably theres a lot here to be deleted.
it is definitely doable in aosp lineage etc roms but flyme os is another thing . you must know exatly what you are donig .
im no developer and i also dont wont to brik my phone so....
as you said devs must shrink the rom down

tool https://forum.xda-developers.com/android/software-hacking/tool-tool-unpack-repack-dat-img-v2-0-t3284806
source https://forum.xda-developers.com/android/software-hacking/how-to-conver-lollipop-dat-files-to-t2978952
guide http://en.miui.com/thread-476300-1-1.html

Okay then. Thank you!

the problem of the large space occupied by flyme is the vendor folder, which other manufacturers are empty and flyme is very full

i used m6 note 4/64, and the system takes 6.67GB. this is incredible number. if you use m6 note 3/16, you ONLY have about 9GB to use. i don't know why flyme os in m6 note is heavy like this. i have used M2 note, and os takes only about 3GB!
so, i desiderate the developer will decrease their rom
thanks you

You should all support the following suggestion, if you haven't do so already:
http://forum.flymeos.com/thread-41685-1-1.html

yeah, i did. i already removed many google app and unnecessary app in global rom, but it does not improve the lot size of the rom

Edited by ippokratis at 2018-05-23 16:40
system is a diferent partition in the internal storege . regardles of how many apps or how many files you delete from system folder , its size will remain 6gb . to take advandance of the space you gained you have to install apps as system apps

my though about the big system size is that there is an aproximately 2gb empty space used by recovery for manualy installing updates .  
i came to this thought after extracting the flyme os update.zip file and then extacted the new.system file and it came to be only 4gb .
also when in recovery mode if you conect the phone to pc a 2gb empty usb space appears

Surely it's an explanation but still, doesn't justify the fact the user is left with little space available.

Worst part is most (if not all) apps continuously generate data that occupy even more space during usage. That's shouldn't have been an issue to consider in the first place.

my internal memory too is filled and I've barely stuff that isn't up to 1.5gb, don't know what took the remaining space of the 32gb