Aznvasions recently released a video covering a shadow buff to Ash's Bladestorm - the tl;dr is that it now acts as a proper pseudo-exalted, where lots of melee mods affect it. While there has been a Savage Silence Bladestorm build knocking around for a good while, this is an overall buff where you can access higher damage with less effort: https://www.youtube.com/watch?v=dRSejZ0zniQ
I of course wanted to test this on Zariman Thrax since I'm stocked up on Mod Boosters and love trying new things. The result was simply slapping the Thrax with a wet noodle, as recorded here: https://www.youtube.com/watch?v=S5z2pnWUZFM
You can see how the Grineer are easily one-shot when Silence isn't active, but it has no noticeable effect on the Thrax and takes forever to chew through their Overguard. Once Silence is active, it does some damage, but not a lot. If it's so slow at base SP levels, it will only get worse at higher levels as their Overguard increases. Therefore, not really a viable option
Even though there are no Banes for Thrax, and Overguard isn't affected by Viral's damage boost, the damage disparity was wild enough that I went into the Simulacrum to try and see what's up. The result is that Thrax seem to have an innate resistance to finishers/finisher damage: https://www.youtube.com/watch?v=RheS5nPKg4s
You can see that without Silence active, Bladestorm performs its animation fine on the Grineer Eximus and takes a chunk out of their Overguard. Meanwhile the on-hit clone damage does absolutely no noticeable damage to the Thrax's Overguard. Once Silence is active, Bladestorm one-shots the Grineer Eximus, and it does some damage to the Thrax's Overguard, but still not a lot
This remains true even when the Thrax's Overguard is gone: https://www.youtube.com/watch?v=wsbFGBlafvg
No damage without Silence, pitiful damage with Silence
tl;dr: Bladestorm is a fantastic trash killer, but still not effective against Thrax or Demolishers
Thrax enemies just have significantly more hp. In the terminal compare it the bombards you spawned. The Thrax have a base hp of 3200 while the bombards only have a base of 300 hp. From my testing all damage is the same, the three initial hits of the ability do the same amount of damage regardless of enemy, and if I was using savage silence the three hits did the same amount of increased damage vs Thrax and Bombards. The slash DOTs were also all the same amount on Thrax as they were on Bombards, silence has no effect on how much bleed damage is inflicted.
Overguard is scaled off of enemy Hp as well, meaning it takes a lot longer to break overguard on the Thrax.
Bladestorm + Savage Silence do the exact same amount of damage vs Thrax and Bombard, you're just dealing with significantly more Hp on a Thrax. As for Demolysts, I'm pretty sure they have ability damage resistance (not sure if its just a generic resist all types of damage, too lazy to test). Ev Trinity does significantly less damage to Demolysts through abilities, its not exclusively less finisher damage from Ash.
Demos have a blanket 92% damage resistance as far as I'm aware
I'll accept the health difference, but there is something very fucky around finishers on Thrax - you can see it if you use Ash's 3 on them both with their Overguard up and down. No finisher option ever options up
With all the buffs available for Bladestorm, Azn's vid (using Breach Surge to get visual access to the clone's on-hit damage) shows that the clone's hit is doing approximately 10 million true damage. This was without Savage Silence - allowing for no Bane for a Thrax, but the buff from Savage Silence, even approx 10 mil should be enough to noticeably hurt a low level Thrax - although it's long winded I can check the damage numbers in the Simulacrum when shooting one of these non-SP lvl 185 Thrax to see that their health at this level is between 800k-900k. So a clone finisher damage hit in the millions should one-shot them. But even once their Overguard is down so Viral is free to take effect, the damage still remains pathetic. Which is what makes me think they have some sort of built in resistance