Your point of cost vs efficacy is valid however the best application of C3i is very different than C3 . To get the most as an attacker with C3i you are using 4 mediums and 2 lights with maybe a 5/8 heavy Calvary unit substituting for one or two of the Mediums . Say 2 Preta light mechs moving 7/12/7 , 2 5/8 Crabs with 2 Er PPC s , and 2 missile boats . The lights approach one on extreme right and the other extreme left flank with the intention of each getting to range 7 of a target . The lights fire and the Crabs poke wholes in the enemy unit and the LRM missile boats exploit them . Assault and slow heavy mechs use with C3i is OK when you are defending a prepared position but becomes too costly in wasted tonnage when you actually use them just like standard C3 . It has the advantage that you don't have a 5 ton Master computer in a slower heavier mech slowing down the whole attacking formation . No C3i unit should be moving less than 5/8 to get the most out of it . With the above example and the vagaries of ECM the enemy could typically put 1 ECM unit on one of the advance units and if the advance unit has ab ECM unit on ECCM the possibility of losing the network becomes remote . The light unit should have a +4 movement modifier and Terrain against the closest enemy and medium range or better vs the rest .
I agree that's a very effective force. It is also very very expensive BV wise. If you don't run it near perfectly or end up on a map not suited to it you'll simply get rolled by a standard force through weight of numbers. Your opponent won't even have to be a highly competent player.
That brings up another point. Blind matches on blind terrain give C3i nets a small chance of surprise. If I know I'm facing WoB - especially MD - I'm gonna swamp the board in ECM. Mainly fast cheap rotary and hover units. The chances for C3i to pay back even a fraction of its BV is negligible.
Even working perfectly a C3i net using cannon units will have an uphill struggle pitting their weakened BV firepower against the stronger armour and firepower of an opponent. The C3i player is nearly always living in hope that his/her opponent will engage in a long range fire fight. Even rookies will run to close contact when facing a net.
I knew one player that played MD with C3i. 16k BV locked into six mechs and he would usually crush opponents with twice his weight of metal on the field. So such nets can be highly effective. But you need to be highly skilled at using the advantages the high BV cost gives you.
A bit like playing Clans in the Jihad Era only even more difficult. I often think it is the 'hardest' setting of this game if you play BV balanced games.