To amend my previous statement, I would say that Elf-A is also potentially a very powerful and viable tree, but it requires the aid of two rather rare CBMs in order to be so: The repair nanobots and the radiation scrubber. Once you’ve got those, Elfa becomes godlike.
Getting back to Weak Genetics though, Robust genetics is almost always gained at character creation. IIRC the only mutation categories that actually provide it are the Slime (which really, really needs it due to Genetic Chaos) and Medical. And if anything, weak genetics as it stands here even more strongly pushes for the Alpha mutation tree, as it has no serious negatives to choose from. It just mostly screws you over if you try a different mutation tree afterward.
I don’t feel like it really adds anything, personally. If you really want to make the other mutation trees more viable in comparison, in my opinion the best way would be to simply add more and better options for XL clothing, which it looks like you already have planned anyway. That levels the field enormously.
I do love the idea of pretty much everything else you mentioned, so I’ll be keeping an eye out here either way. 