I don't think any folks are discussing ECM on the basis of "realism" or "how it should work in the real world". The entire game is based on Battletech physics which needs a good helping of "suspension of disbelief" whenever you log in.
The main problem with ECM is that it is a hard counter to two weapon systems .... LRM and SSRM.
Have LRM ... opponent no ECM ... LRM boats are king.
Have LRM ... opponent has ECM ... LRMs do nothing.
It is almost impossible to really balance LRMs in that sort of environment.
They either need to do lots of damage so that when they get a chance to hit through ECM they can do some damage or they need to have a lower damage so that when there is no ECM they are not overpowered. The problem is that LRMs can't be both so they are somewhere in the middle. With ECM, LRMs are subpar but can do some damage and if there is no ECM then LRMs can be OP.
This all results because ECM is a hard counter.
Now lets consider the other abilities of ECM. It can shelter the entire team within 180m so that they are all invulnerable to ECM. No one can get locks and the only way you can even see the other team is if you look very very closely.
Now, ECM probably also made it harder to build MWO aimbots since they can't use the targeting box to reliably aim at the center of an opposing mech.
This was exactly how the game was when ECM was first introduced. It was brutal.
PGI then started to introduce some counters to ECM ... TAG, NARC, PPC disruption, UAV, BAP
TAG draws a straight line all the way back to the spotter ... so they can't spot for long.
NARC has improved but it still weighs a lot and the rewards for using it aren't that good.
PPC ... you have to hit the ECM mech and it is only lockable briefly
UAV ... awesome until it gets shot down
BAP ... essential for SSRM mech ... but limited range means that you have to brawl or skirmish to get in range of enemy mechs
ECM stacking can make it difficult to suppress ECM if they have more than one.
PUG matches have NO control over ECM balance ... each side could have 0, 1 ... 6
... so you roll dice on match balance when ECM and LRMs are considered.
Redesigning ECM will REQUIRE redesigning LRMs and likely the entire mechanism of locking and sharing targets on a team.
Anyway ... the complaints you see on the forums have nothing to do with how some device should act in real life ... they have to do with 2 things
1) the current design is a broken game mechanic (but I would like to hear from PGI about the reasons for the design choices they made ... there could well be some specific reasons for that design choice that are not obvious to the community)
2) In the Battletech source material ... ECM does not work the way it has been implemented in MWO. MWO ECM actually combines the effects of at least 3 different pieces of Battletech gear ... since the MWO balance started out based on TT values (look at the weapon damage values if not their rate of fire) ... the question becomes why was ECM implemented this way and what can be done to make the weapons and equipment more balanced and fun to play.