Disclaimer caveat-- I'm listening through not-too-expensive headphones from an iPhone 6S. So not the top-of-the-world monitoring chain, still:
I don't hear the vocals as overly harsh. They sound like vocals. Now, is it possible to make some tweaks? Yes. Are there possible problems with your process? Yes. I will tell you what I hear, and hopefully others (maybe some of my experienced-ear compatriots here) will chime in as well...
I do hear some "spitty" sibilance/distortion. Are you using a pop-screen? You definitely need some kind of windscreen or pop-shield with any decent condenser microphone. The moisture from your breath can overwhelm the element and cause issues for your recording as well as your mike long term. If you're not using one, get one (and I would guess not, from what I'm hearing). Also, how are you setting your levels on the way in to your DAW/recorder? Make sure that you are not clipping on input. I don't hear a lot of room in your track, but you can always go for an even dryer vocal when recording by creating some kind of vocal booth in a closet, or even throwing a blanket over your head and the mike or making some kind of "recording tent" when you track vox. As to microphones, you are picking some decent stuff and I think the problem is in your application and/or input chain somewhere; you just need to keep trouble-shooting until you figure it out rather than buying more and more expensive microphones. Otherwise I see you possibly maxing-out a credit card on a U87 and still not being happy.
If you don't want to get a new interface with a more all-in-one feature set, you might want to consider a microphone preamp or some kind of channel strip with more EQ controls and other helpful features (variable input gain and/or ohm settings for various mikes).
On compression ratios for vocals-- modern sounds tend to be very compressed. You may want to experiment with anywhere from the 6-to-1 to 10-to-1 range. Over-compression sounds terrible, but if there is not enough, too much dynamic variation makes the voice hard to mix and "sit right" in the music.
Regarding room treatment (again, I don't hear any major issues on these tracks, but just for the sake of thoroughness), it sounds like you've put up some appropriate measures, but did you actually go through a room calibration process, or did you just buy some random treatments and sort of "eyeball it?" Spending time on the calibration can make a big difference.
I can hear what sound like your edit points. This may not be a big deal, as those things tend to get buried in a mix, but best practice is to make those as smooth/natural and breath/click free as possible. Think of your entire recording and mix as layers of varnish on a woodworking project (a great analogy I read once). In the finished product, you can't necessarily identify so many individual issues as you can that the whole thing "isn't right," conversely if it sounds great it is the sum total of all of the individual "layers" and "brush strokes" of sonic varnish over the entire project. So each little step either helps or hurts, depending on the amount of time and care taken.
Finally, you said that you are adding vocals to "remixes." What are the source tracks for these remixes? Are you actually mixing multi-tracks or stems, or are you just making loops from instrumental sections of pre-mixed stereo tracks? It is _very_ hard (but not impossible, I suppose, maybe for Dave Pensado) to get new vocals to sit right on top of a previously mixed and mastered stereo track. Everybody who has tried this has come to the same conclusion. If that is what you are doing, it may be part of, or the entire source of your problem.
I hope you figure out the sources of your displeasure without spending too much $$$$!
GJ