I'm becoming more confident, and with that confidence comes clarity.

I rebuilt the above page from scratch. Yes, I copied the layout, so I was much quicker, but I wasn't bringing any problems from the first attempt into this one.

Mixing Flexible with Freestyle, I had no 'where'd-it-go' moments, and nothing that made me delete a Block and restart. In short, it all worked as expected. Now, onto the niggles:
ONE) Marquee selecting. I know I can use SHIFT click, or select from the P&L Gallery, but the amount of times I instinctively drew a box...
TWO) Moving multiple objects in a Block. I've never taken drugs, but if someone asked me what I thought it would be like, I would tell them to open Xara.
THREE) Snap to objects. Aligning things in the Freestyle blocks is sheer guesswork, especially when combined with the above.

Things I feel certain Xara will add in the very next update, probably within a week =/
ONE) Key press and click to add an object into a Block. As an example - I paste an object, it appears over the block, but not IN the Block. I position, colour, resize, and then I have to drag it away from the Block, release it, select it again, and drag it back into the Block again.
TWO) Toggle from Freestyle to Flexible, and visa-versa.
THREE) Ditch the forced variant idea, or explain why it's a necessity.