TOUGH = 100HP, 10 energy, adds weight
MOVE = 100HP, 50 energy, gives move
If you see both bodyparts next to each other, you can see what I mean. The 40 energy you save cannot make up for to the (useless) weight it adds. On RCL8, you have 12900 energy available, 25xM,25xA costs 3250 energy. You basically could build nearly 4 of those (missing 100 energy). This gives you 25 Parts of buffer before your ATTACK suffers. Now if you build something which we could say is somehow similar: 15xT,10xM,25xA you pay only 2650 energy. 600 Energy saved, but 300% movement speed lost (and even worse on swamp!!). And you would only be able to build 5 creeps for that (350 energy missing).
If you are defending, this movespeed might perhaps somehow work, but if you are attacking it probably won't. And *if* I defend, I'd rather go 10M,40A instead of the above.