Okay, I see what you’re trying to do, but I might suggest going about it a different way. Granted, this is a fairly limiting view of your overall approach, so I’m interpolating a bit (read: making assumptions).
I would separate the concepts of rotation and velocity a bit further. Your “arcing” or boomerang-style motion is really more about location than rotation. For instance, if your blade went straight out to a point and back on its X-Axis, but moved in positive Y on the way out and then to negative Y on the way back, you get that arc. Therefore, my blade would use a Component hierarchy (parent the mesh component to something like an Arrow) where the arrow handled all the location adjustment.
So let’s just focus on that for a moment.
The moment the blade is thrown, you need to lock down two things and store them in vector variables: the start point of the throw and the end point (that’s the most distant location, not the return point!).
I think you’re getting these from components on the character (which is probably what I’d do, at least for starters) using something like Arrow Components. So you’re basically having to send those locations over to the BladeBP and they get calculated first thing. You need them calculated prior to the Timeline updates because they’ll need to remain constant. If you update them throughout flight, the blade will move with you in a fairly unrealistic manner (maybe you want that??). I would do that on the way back.
So you lock down those two positions, then use a Timeline to Lerp location from the start point to the end point. On Finished, you switch to a second Timeline that Lerps on the way back, but this time the B point (target) of the lerp is the player. In this way, you get that “Zelda boomerang style” style motion that flies toward a locked point, but then flies back to you.
Spinning the blade can be separated, because we handled motion off a helper (Arrow) component, to which the blade is parented. We can just offset the Mesh’s location/rotation from that parent and get any kind of rotation we’d like.
I realize this is a lot to play with. So I’d start by making a simple blade that went to a world position and back. Then start layering on the tracking behavior to make it return to you, then start layering on the arc, then the spin.