Now that I have thoroughly listened to both (having used V14 for more than a month as my daily driver and the Monarch for 2 weeks daily), I personally prefer the Monarch as it has a "better overall package". I say this in quotes because a better overall package for me is something that has good bass that goes deep when needed, realistic mids that has a good bite/attack when I need (I listen to a lot of rock and funk songs) and highs that has good extension and air. And I say this with Monarch on stock cable (2.5 to 4.4mm balanced) VS a V14 with PWAudio Xerxes 8-core cable (4.4mm balanced)
The V14 is a good earphone if you want something a bit more balanced, where the mids aren't laid back and you still get decent highs and lows. Mids on the V14 are definitely a tad better than on the Monarch as it has more presence and thus having more of that attack I get in snare drums and bite in electric guitars. Due to the more present mids, vocals have a greater authority, when the singer belts out higher notes, it really hits you and you feel it.
However, the Monarch though with laidback mids, still retains that similar quality that I described above of the V14. It just sounds "less audible" on the Monarch due to the V-shaped tuning so it doesn't hit you as hard as the V14. I do like the V14 when I wanna fully enjoy guitars and vocals only or if I am trying to do more critical listening (as everything is a bit more balanced on the V14), but then again, I listen to my music as a whole, so the Monarch is more suitable. The Monarch has bass that goes REALLY deep and the V14 doesn't quite achieve that, it still has that "BA bass" though with some semblance of DD qualities, but then still, it ain't a DD bass sadly. Vocals are more forward than the other instruments in the mid range segment on the Monarch so if your concern is just vocals, then no worries on that. Yes you can still get the highs and lows on the V14, but the quality and extension of the Monarch is just so much better that I feel is only achievable by using dynamic and estat respectively. To add on to that, the Monarch just has way better detail retrieval and layering to me so though mids sound softer, I can still easily tell apart the different instruments. The experience I get with the V14 when listening to really deep lows is just "Oh wow, not bad for a BA driver!" but on the Monarch is "Oh damn, that's really deep" and you get goosebumps from it.
Hence, the Thieaudio Monarch is just a better listening experience overall for me! However, if you want something a bit more balanced, then the V14 is also a good choice! Neither is bad, it's really a matter of personal preference here. The Monarch sounds closer to studio monitoring speakers, while the V14 is a technical BA earphone. I have also been very used to a tribrid sound (as my last few earphones were the M5 and Noble Khan) and a full BA setup can't quite fulfill my needs in the highs and lows segment anymore.