Depending on which deck you are using, and the relative system of astrological associations you subscribe to, interpretations can vary greatly, especially regarding the Court cards that so many people have differing opinions.
The Hermetic Order of the Golden Dawn attributed the Knight of Cups to Pisces, which is a complex sign of self-delusion, romance and an inner realm of fantasy that can conflict with reality and feasibility at times. I would say your conclusions are accurate regarding this card, though some of what you say seems to point to Four of Cups, as well.
I believe the Knight of Cups probably has the best intentions in mind, though with the lack of conviction needed to follow through with things due to an inherent inability to solidly commit to a cause from a lapse of reality. One could also attribute this characteristic to the mutable aspect of Pisces, which is an easy going state of mind that could go one way or another, versus the initiative cardinal signs and the committed fixed signs.
Another system of astrological attributes, including Thoth and the Waite decks, have assigned Scorpio to the Knight of Cups, which opens a whole other confusing can of worms. As Scorpio can be committed almost to the point of obsession, it's difficult for me to subscribe to that link with this card. Something would have to go horribly haywire like treachery or deceit for the Knight of Cups to lose sight and interest of his target. Thus, I am going with the Pisces association, but your mileage may vary.
Just my two cents here, but I think you have it right. Though, I do believe that the Knight has integrity and probably wishes for a solid commitment, lack of focus and conviction strays him from the path long term.