As a very practiced conga line player I think folks are severely overestimating ECMs. They exhaust on use, so it will only help you for one attack per turn. The real strength of the conga line is that it is really tough to approach without being in multiple firing arcs. One use of an ECM is not enough to be able to barrel right in. Bracing one attack out of four will still get your ISD killed.
Blocking is a good plan, but harder than it sounds with minimal margin for error.
I have had the most trouble when someone can maneuver to force my lead ship into multiple overlapping arcs. Plan a trap and set ships up where the conga line has to fly into overlapping arcs of its own.
Even if an ECM holder is bracketed by four different attacks, ECM can reduce one of them. Approaching two Assault Frigates with gunnery teams means I'm probably going to be shot twice, and I'd like access to Brace for at least one of those attacks. Even being shot four times out of a corner I'd probably kick it on the first four-dice shot that amasses a lot of damage. Same with MC80s, though defending on that one is going to be tough.
I just think the ability to reduce incoming damage this way is incomparable, and ECM helps guarantee that ability for anything other than an Intelligence Officer watching you. Even so, you can still kick it in spite of IO to handle atrocious damage amounts. Just as long as the ship burning the brace has a very good chance of seeing it's next activation to vomit damage, or if it will force another opponent's ship to use one attack and finish off the ship that just discarded the token, I think it's worth it.