It's a very fundamental shell on paper. And at the very least I think that para plus hairball is better than filia plus mk bomber. Though at this point I think people will call me stupid for that one...
Actually although pillar/hairball is an amazing shell for assists, (in a very similar way to updo/buttslam as clarence pointed out) good assists does not necessarily make a good shell, there are a lot of other things to consider in terms of team order/options when coming in/dhcs etc
Now for x/para/filia the dhc synergy is VERY different from x/filia/double. One of the glaring issues in this shell is that parasoul's level 1 supers aren't the most damaging and aren't that good for finishing characters off like for example fenrir drive dhc, you may need to either go for additional resets with your point or else burn the extra bar for the level 3 (which ill admit isnt a bad idea at all, but you still spend a bar that could go elsewhere eg scalpels).
However despite this bikes dhc can be pretty safe and be a way to spend some bar to get parasoul in and allow your point to recover some health as opposed to filia dhcs which are pretty much all unsafe (although you can spend the 3 bars to get double in with catheads which not a looot of people do (it isn't 100% safe it can definitely be stuffed) but I sometimes do if I want to get peacock out). Along with this, dhc into level 3 with egret call is far too good to ignore for reasons that should be pretty obvious. The unsafe dhcs with filia also become a problem when the shell is forced to fight it out alone.
The other weakness in this shell is that parasoul is undoubtedly weak when she comes in after the point dies with no air reversal or any real options for escaping incoming setups. Along with this she can sometimes have a harder time dealing with pressure due to having to hold down for her go to reversal (you can charge it on incoming and go once you hit the ground but thats about it) coming in after the point dies instantly puts her in a bad position. This is not the case with filia who has access to gregor to try to stuff setups (and even though filia is in this setup she is in the anchor position which means that you would have to have lost your point and parasoul before you can do this). Also with double in the back you can go right into catheads if you so wish (once again not 100% safe but occasionally a good option). Double has trouble on incoming too but she does have more options with double jump and level 5 if you reaaaaly want to burn the bar.
Also anchor double > anchor filia due to many of filias options being limited by lack of assists (eg harder hitconfirms/pressure) whereas double is more self sufficient and has more ways to play around with meter.
Overall it is a very strong shell but it definitely has some drawbacks in comparison to the fil/dubs we know. I see it as more frontloaded and being able to spend less meter for getting characters in but spend more for dat damage where as fil/dubs is much more self sufficient in the late game and the meter spent on damage is lower (although meter spent on utility is higher). Which one you pick really depends on your priorities/preferences as the are both pretty ridiculous. Also a reminder that having a set of two amazing assists isn't always the best shells, I mean look at the shit that is dubs/pw, it tends to be much more backloaded (with pw's mediocre assists) but it is still one of the scariest things in the game right now.
(also sorry for this not strictly being about duckator but this probably belongs in this conversation. I guess you guys could move this to a different thread if you felt it to be more appropriate)