Roar vs Eclipse, comparing the two based on where they'll be at a proposed 30%:
Eclipse is a multiplicative 30% damage buff to only yourself and only your weapons. With an augment it can buff allies as well, but only while in range. This is compared to 200% at base. It also only costs 25 energy and has the option to be used as a defensive ability, but we'll be ignoring the details on that up here because that's not what the vast majority players use it for.
Roar is also a multiplicative 30% and without an augment it applies to your guns and abilities, as well as all allies in range when it's cast for the full duration, and even your pets, and it's a 50% boost at base. It costs 75 energy.
For the sake of simplicity I'll assume that eclipse will function like a faction style multiplicative bonus like roar and apply to damaging status effects done by your weapons.
When would players actually choose eclipse over roar with these changes?
When they have a frame who does no ability damage, has a low energy cap/bad energy economy, or when they want the defensive ability of it and are playing solo. I mention the "playing solo" portion there because in a group, you would want to buff your allies with the eclipse augment, which means you're giving up a mod slot that could be used for the superior damage reduction of adaptation, which is tradable and can be obtained by any player.
The nerf of roar is a 40% overall reduction in power when used via helminth, the nerf of eclipse with the proposed 30% would be an 85% nerf when used via helminth, which is absolutely excessive and out of line with what the helminth system normally feels like to use.
What number would make sense?
Obviously the desire from DE is for more than the nerf roar has due to the added reliability and higher number, if it works the same as roar but only for weapons that's okay. But that restriction of it only working for your weapons means it should absolutely be a stronger buff than roar for damage. Given the current numbers and plans for it, I would suggest keeping it at a buff of 60% but only if DE plans to revisit it and buff it if needed. If this is going to be like so many situations where the change is released and left as is for potentially years, I would much prefer seeing the buff be released at 100% in order to ensure that the buff still feels good to use in areas where it's dominant currently with the 150% buff that can be guaranteed via lighting snapshotting with invisibility, heat procs on yourself, etc.
I'm glad that it's no longer going to be additive and an entirely useless ability, but if it's made to be "roar but cheaper and worse" then it will simply be replaced by roar, or xata's whisper, in almost all cases. If the goal is to indirectly shove more players into using "group buffing" abilities like roar, then this change would accomplish that goal. If the goal is to encourage greater build diversity, then the numbers should be at least a fair amount higher than roar's buff to ensure warframes that have both ability and weapon damage will have some incentive to take eclipse on occasion.