Did some testing with Stormriders/Subterraneans.
Devastation reduction seemingly caps out at 75% for Subterraneans, so it takes 4x as long to make your colonies within storms utterly worthless. This is good for general use, but still means permanent storms are a useless feature because you shouldn't keep them around longer than necessary anyway.
For Stormriders, it'll cap out at 83%, with 98% for colonies in a sector governed by a Commander and 100% for the actual planet the governor is on. Commander governors do have a specific downside and upsides that aren't broadly applicable, so this means one planet per Commander can be functional in a storm where you're largely trading governor bonuses for storm bonuses (unless it's a worker world, in which case you get both). Note that this also means you'll have far fewer admirals actually leading fleets, if any. But it at least becomes viable for these specific planets, storm bonuses can easily exceed governors.
For those in the sector, 98% reduction is sufficient to make very heavy although not permanent storm use viable. Unfortunately, given the governor situation, this means Stormriders become drastically worse at using their core mechanic when they go beyond a sector or two, and permanent storms are generally useless past about 5 colonies.
I am, to be clear, not opposed to storms causing some devastation - that seems like an appropriate mechanic. But slowing down the devastation gain while designing storm-focused empires around keeping storms active permanently and in their space through the AP and civic-unique buildings is useless, you can halve the rate at which my colonies become worthless (via planetary shielding) but for the empire with (locked) storm-focused civics, this changes nothing - colonies inevitably becoming worthless is not a good thing. It doesn't help that the other use for storms, combat effects, is gone by midgame because you can get 100% removal of those effects without even a component.
I therefore suggest the following fixes:
1. Make the techs for storm effect reduction apply to both offensive and defensive stats (effectively reducing the number of them by 50%) but also reduce their effectiveness to 30/60% so they no longer completely negate this effect. Add an aux component giving a 20% boost (in other words, negation at two such components, buffs in storms at 3+).
2. Change all devastation gain rate effects for storms to also lower the maximum devastation by an equal amount. This means if no other changes were made that most empires would cap out at 50% reduction, which for reference is a 50% reduction in job output, housing, amenities, pop growth, trade value, immigration pull, and job upkeep. Note that the nuke to housing will reduce growth even further, as will amenities reduce stability and reduce job output even further, which means a 50% devastation cap is still going to make planets effectively worthless. It is a much more potent effect than habitability. It also happens to be the threshold at which planetary FTL inhibitors stop working, which (appropriately?) means storms can be used to disable these. This will, for empires without unique storm bonuses, make permanent storms useless despite being broadly available (this entire mechanic already is, but I'm emphasizing that this will still be the case).
3. Change the Stormrider devastation reduction on Commander governors to apply to ALL governors. This still means you'll need a governor, but will now be able to use any leader type. With the above fix in (2), 98% reduction for the entire sector now leaves the planet functional but with a modest debuff, while the governed planet is just fine.
4. Add devastation gain reduction to all storm-focused civics and Galactic Weather Control. Note that with (2), this does NOT need to hit 100% to be effective, but an empire focusing on storms should at the absolute minimum be able to hit a 60% devastation reduction. At 40 resting devastation in a permanent storm, you have some massive penalties and some upsides if you accommodate storm bonuses very well, at least for some storms, some don't do enough to compensate for the penalties in output alone. I suggest each civic and AP grant 10% devastation reduction, which will hit 60% with any one (still VERY BAD) and with a non-Subterranean, non-Stormriders empire will hit 80% reduction if you have Storm Devotion, Astrometeorology, and GWC. Or 90%, if you also have Planetscapers and it counts (it probably shouldn't, but it does have a useless storm protection effect now). This is still a 10/20% penalty to the things listed in (2), which is a massive penalty in exchange for whatever the storm happens to be improving. This also means a Stormrider empire with any two civics and/or GWC is immune to storms devastation, but that just seems appropriate. Subterraneans would then be able to achieve this with any combination of three (or the ONLY combination of three, if indeed Planetscapers wouldn't count).
5. Optionally, because without playtesting I'm not sure if this is or isn't necessary, reduce positive effects from storms a bit. The devastation gain is currently an inevitable timer to worthlessness that is at odds with how the mechanic is designed to keep storms around, but the positive effects may be too strong as well. As an example, Gravity storms give +50% output to enforcers, administrators and entertainers. This possibly too much, although given the level of investment required to actually negate devastation under my proposed system above perhaps it's just fine. Like i said, it would need playtesting.
This is just my version of what I'd do to fix the mechanic this entire DLC was built around, you obviously don't have to literally do this, but the problems broadly are that storms are designed as something empires focused on them want around long-term, which they absolutely do not, and that fleet effects from storms are effectively not a mechanic by the time you could deliberately weaponize them with the AP because the techs allow no-investment negation.
Oh, and a final problem note, but this is possibly just a bug; reducing storm devastation gain by 100% (via Stormriders with a planetary shield and a Commander governor, currently, although presumably also with any other method if one were added as above) doesn't allow devastation to decay. You're still "gaining" 0 per month, so therefore it won't decay. Also, Shroud storms don't appear to be something you can create. That's kind of odd considering they seem to be designed for Psionic empires to want but they can't really do anything with that but hope with RNG. It's also possible that the general player-unfriendliness of how Psionic is currently designed has stopped me from having a Shroud outcome give me such an ability.
