Exactly, it's not known and Merlin using Gowther instead of doing it herself suggests that she's unable to.
Merlin stated it herself that her Absolute Cancel couldn't completely erased Gowther's curse, which is why she made the armor.
Because the difference in their profession matters a lot? There are powers that are specifically used by magicians (Teleportation, Perfect Cube) while there are powers specifically used by warriors (various sword beams/slash waves). Thinking a warrior like Haru using a magician's specific skill, while can't be said to be impossible, should be the last thing he's trying to piece together.
Also, it would make more sense to link Haru's Runesave with Meliodas' Counter Vanish. Absolute Cancel completely erased the magic, leaving no traces of it after being cancelled. Runesave however has the property to 'cut' and 'seal' whereas cutting the magic usually more like dispersing it, as in there are scattered insignificant portion of the magic left (like when Haru was parting the tsunami, the water was more like dispersed rather than completely erased as they are not entirely gone). So it looks similar to how Meliodas used Counter Vanish and dispersed Cain's flame, since there were scattered piesces of flickering flames left that wasn't completely erased. It also make more sense since Haru is a swordsman like Meliodas instead of linking it to Merlin.
Unless the OP says that it's equalized, then it's not, and Haru isn't blitzing Escanor anyway. A good speed advantage, yes but it takes more than just doubled the speed to blitz.
About paralyzed and ignore damage:
- Form 6 - Mel Force: The sword of air, this form allows the user to fire powerful bursts of air at the enemy to blow them away and paralyze them.
- Form 9 - Sacrifar: The most destructive of all the forms, Sacrifar is a frightening blade of bloodlust that trades the user's emotio and will for the power of Carnage. As the sword was not made for Haru (but rather Shiba), the sword will take over the user after sometime. The sword gave him an enormous increase in fighting abilities, allowing him to effortlessly overpower a powerful fighter like Lucia.
The 'ignore damage' part was referring to Haru. In Sacrifar, he becomes bloodlusted and loses all emotions except aggression, he was unphased after taking Lucia's explosion and actually smiling. He wasn't able to control it back then but he's capable in the final battle after gaining the 10th form Ravelt.