Remove all forms of slowdown till your competent, so leave it off forever.
So there's a lot for this. So basically, slowdown shouldn't exist and here is why in a quick fashion. It does nothing beneficial and only hurts the player.
First, the clip here showcases a bug that occurs when slowdown happens, where the unit can't make the jump. Considering the developer graciously artificially inflated the difficulty by removing 30-50 seconds on the lobose kill your mechanic, this is actually a problem when it occurs. If the developers weren't so keen on screwing over players for 0 good reason, it wouldn't even be that big of a deal, but, they are a shit company and developer, so what can you expect.
Second, even if they didn't do that nerf, slowdown has always been an issue regardless, since if you go through training dummy, you can practice your skills and you'll notice a complete lack of slowdown, so your SCs work as normal in real time, no problem. In actual combat, unnecessary slowdown after beating certain enemies, not even a full clear, just certain enemies, can trigger a slowdown and harm you and the easier one to showcase, when using Skill chain moves, a banner with slowdown appears while the timer mechanic still goes at normal speed. This drains around .5 seconds of time off your clock per each SC move used, if you use more then one near each other, the delay stacks. Since they have it just fine on training dummy, there is 0 reason for this to be there outside of being a hindrance. This is negative in raid, orbital lift, kamazone, you name it.
The last one and this one doesn't do too much, but it's still cheap garbage none the less, kind of like when someone throws a bomb after a fight is done and the AI grp to it and take damage from it, which, this is basically similar. While a slowdown is happening and since combat is done, if one of these effects is active, you'll be in slow motion while it's in normal speed. Since you can't dodge and are being slowed, it's very likely you'll suffer some damage from this, but usually you'll have something to combat this bullshit, like a healer on your team or it's just not that big of a deal since the difficulty might be derp easy so you take no damage. Still bullshit none the less.
The excuse would be, since the community's collective braincells would equal 0, that the argument is that it's CooL! /shades. So despite the fact it causes bugs and only hurts the consumer, it doesn't need fixing, a situation if you look into it, will showcase the self centered greed around the upper player base. If it isn't hurting me specifically in a big way, I don't care, but I'll defend the developer if someone else mentions it. Faulty logic to a T.
Probably one of the easier topics would be conquest, which is still a dumpster fire, but now 2 year end game players and whales can actually finish it all, so it's "Fine." Despite the fact that even if you fully complete it, it's still a worse version of raid, with trash mobs, 2 gimmick boss fights with poor programming, then the final boss being fine outside a few hiccups. Basically just a glorified waiting simulator as you do a worse version of raid with 3 interval bosses, with a more powerful repeat if you go all the way. Considering the rewards are worse, shoulda just made the 3 bosses raid units and not be a garbage developer. Or, be competent when making Conquest, don't want too many miracles asked though.