FDEV beta tested diminishing returns on HD shield boosters years back, but didn't go through with it. That would have taken down the hitpoint inflation and made resistances more important.
As I recall it ( I might be wrong here), they announced it for beta, and then the outcry was so big that FDev did not even test it in beta.... which is sad, as that is what they can do in betas, tests how things works and see what people do with it... not everything in beta needs to be approved for implementation...
[rant about stupidity of shield booster engineering]
E-rated heavy duty, 2T (0.5T), 50.7% (4%) boost to shield, draws 0.25MW (0.20MW)
compared to
A-rated heavy duty, 14T (3.5T), 73% (20%) boost to shield, draws 1.50MW (1.20MW)
Somehow E-rated boosters can be enhanced almost 13 times from its original value, while an A-rated booster can only be increased almost 4 times....
And that is because the boost from the engineering is not BOOSTING the actual value, but ADDS to the actual value.
ie.
Engineering is not to affect the current value of the shield boost, ie. if the engineering was give 50% more, it would make more sense for it to work like this
4% boost increased by 50% -> 4% *1.5 -> 6% shield boost! not as it currently seems to works, 4%+50% -> 54%
There is a huge difference between 6% and 54%.... or 9x the difference....
and if we do the same with A-rated
20% boost increase by 50% -> 20 *1.5 -> 30% boost, not as it currently seems to works, 20%+50% -> 70%
And yes, this would mostly make the E-rated, D-rated etc shield boosters pretty useless, now they are valid, since engineering still gives them a really HUGE boost with out very few of the negatives.. like much less impact of their mass...
[/rant about stupidity of shield booster engineering]