If you cost the EC thunderhawk for fearless, and call it an 'Emperor's Children Thunderhawk' then all is good
I'm not trying to sneak changes into any other lists here....
The issue as I see it, is of differing metagames, I seem to recall Dave or Ruth saying that in your group, you don't usually thunderhawk terminators in? and in general from your batreps, it doesn't seem that you play a heavy air-assault sort of game, a cursory glace at some recent batreps shows a single thawk in most lists, normally with tacticals inside
in our group, we typically play an air-heavy game, most of my successful marine lists have a pair of thawks, usually loaded with at least one terminator formation between them, sometimes one each, dptdexys, miket and steve54, all tournament winners and much better players than me are in the same boat, having fearless on the thawks jumped out at all of us as a very potent addition to an already potent unit
as air assault can be so devastating, there have to be some concessions and increased risks, the aircraft having the lethal critical effect for example so you do occasionally lose the thing with all hands before it gets to its target, and another risk factor is that if the assault doesn't go your way, you typically lose the thunderhawk, as you probably should, fearless removes this risk entirely, if the thing is loaded with noise marines or whatever, you can chuck it in at any target, safe that even if you lose the assault, your thunderhawk will be flying off unscathed, and the formation inside will need to be killed rather than hacked down
the other factor which I did flag up in a batrep is a broken fearless Thunderhawk can only ever pick up a maximum of 4 BMs rather than 6 for a regular marine one, and in practice is more likely to end up with 2-3, which means not only is it not at risk of death by proximity, it is FAR more likely to come back on next turn
I've already suggested they be tested at 200 points, the same as the non-fearless, non-ATSKNF DC2 vampire
I'm putting some lists together, and after I finish my share of the IF testing I'll run a few EC and RC batreps using thunderhawks and compare them