Union MultiArrayList even worse in safety builds

So if I have a tagged union with 64bit fields and u8 tag, total size of the union due to padding will be 128bits. If I need a list of them and I use array then I am wasting 7 bytes per element. Now MultiArrayList should fix this and it does but only in ReleaseFast builds. Debug and ReleaseSafe builds, that I still care about and that are already struggling now get even worse, since now in MultiArrayList I have a list of u8 tags and then additional list of 128 bits elements where 7 bytes are was...