mpdf is pretty new in Tiki and as I don’t use it myself I can’t tell if it is "broken" or not.
What I know is that people (corporate company running Tiki) are using it successfully.
It may require some knowledge to tweak and do final tuning but, that’s a kind of normal for an advanced feature.
While I understand your frustration, I don’t think it is fair to blame Tiki.
Unless you do basic things, any webapp will require developper, configurator or webmaster skills at some point.
There are hundreds of Wordpress (supposed to be 3clicks running, super simple) specialised freelancer (coder, designer, websmaster, IT Admin, etc) that are making much more money than we do on Tiki... There must be a good reason. ;)
But back to your website my point was to save you time.
In the end it’s like many task we have to deal with.
Or you have time to learn and experiment or you pay someone else to avoid wasting time and focus on your project.
In any any any case, we’ll be sad to see you go away. ;)
PS : I went at http://seeds4c.org/Ubuntu+16.04+LTS+for+Human+Beans to check the image issue. It worked fine for me on Safari MacOSX. (I could see the pictures)