I agree. Using ECs for defense, unless its really your last try to defend, is just suicing your account. Their numbers look good. But if you take into account the costs and upkeep, they are just a waste if you defend with them.
You need the for attacking.
As for offensive Roman inf. If you are active and raid a lot, go EIs/ECs (depending on your activity, raidings, overall effeciency and development) and make Imps to clean players and impose your will. If you are not as active, raiding with Legos is fine. You can build them along with praets to form a nice defense in case you have a few offline hours.