For the first one, the voice feels a bit out of sync and the instrumental overpowers her a lot. Defoko is a very airy UTAUloid so you're not gonna get a crispy clear sound from her, but I recommend searching for mixing tutorials here. While mixing, I usually keep a track with the original song for reference and try to get the vocal track to sync with it as closely as possible--- same with the instrumental track. Once they are all synced, I mute the track with the original song. If you're using an instrumental track where it's just one track without the vocals, I recommend not adding any effects to it as it is already mixed, but instead try to make the vocal track sound like it fits with the instrumental---again, keep the original song in a separate track for reference!
For the second one, I've already commented on it. Blend the notes a bit more
View attachment 9421
You could also try a VCV voicebank which is made so that the notes flow together nicer.