I don't think GameMaker is a joke at all, some great games have been made with it. It's just not built to be a base for a fully functional 3D animation software, let alone to the ambitious scale that Mine-imator is. Admittedly the joke here, is that Mine-imator (and Modelbench, even in the complete rewrite!) continues be developed with it. GML (GameMaker language) is the only real language I know to a proficient level other than GLSL ES for writing shaders for Mine-imator, so it's stuck in GameMaker for the foreseeable future. I plan on leaving development whether there's another dev or not after 1.3.0 or following bugfix patches as I would like to move onto other endeavors following the possible next year of development for the next major update.
In the meantime, I'll be looking into possible optimizations throughout development since there are a handful of opportunities. So far, Mine-imator 1.3.0 has been updated to the latest GameMaker runtime (Was held off, as newer runtimes would usually break stuff due to possible runtime bugs.) which has given Mine-imator a somewhat-noticeable performance boost, which is very present on startup as it's been reduced by about 20 seconds on my computer.
Mine-imator a single-threaded x32 application, as with almost all games made with GameMaker. Rendering all but one core on your CPU and anymore than 4GB of RAM useless in terms of performance. All mesh generation for objects, including bending body parts is done in the same thread as everything else in Mine-imator, causing a slow-down between rendering frames, ultimately dropping performance.