Having eclipse be a damage multiplier should be preserved. It is a very strong ability but it alone does not make a build, you still need all the base elements of mods in your weapon and warframe. Having it be a reliable damage multiplier would not change any gameplay for the worse, things would just die a little quicker, it could also allow for more flexible modding if it enabled players to hit damage breakpoints for killing enemies a bit easier, and maybe with a bit more variety of weapons. Nuking everything in the game is already done without eclipse.
Having eclipse being changed to only give base damage would also be a big blow to Eidolon and Profit Taker speed runs. It is a BIG deal. These are areas of the game that have YEARS of development, and especially in the solo category, it almost completely denies the damage necessary to achieve similar times. Having abilities that give more damage than others is not a bad thing, especially since that's all the ability did in this context, a flat multiplier for weapons damage.
And to address Pablo's comment about it being capped at 350 for helminth, if that's so then there would be almost no reason to use that ability as a damage buff, since as others have said, a simple arcane does more than that. It would be completely outclassed by so many other abilities. It would take the ability as a damage buff, from A/S tier down to C tier at best. I'm hoping that he just misspoke.
Please reconsider your decision. Thank you.