I tend to think there are too many canon mech types, especially variants. I want to know what the main production lines are, but see zero need for the prototypes, experimentals, and one-off Solaris stuff. The first two should be covered as a fluff text in the relevant unit entries. The last has no need, as absolutely anything could be a unique Solaris (or battlefield salvage frankenmech), and is better left to letting players come up with their own. Basically, if only a couple were ever made, they don't deserve to be in a book.
It feels to me like they decide they need a new book, so run up some designs, semi-randomly assign them to factions, and print the sucker. I'd far rather that they first decide what the factions needs or can make, explain this logic to us, and declare which production lines, if any, are being taken down. Tell us why we need this nifty new design, when there is already a Stinger or Warhammer that fills the exact same role.