I think Charlotte should be given a dukedom, as the child of a monarch (I expect), just like her brother.
I don't think Jack should be given a title just because he's marrying a princess... but hey, that's exactly what happens when a prince marries a lady, she becomes a princess, so my thinking is a little fuddled there! In the 21st century, it's a bit of a minefield; things were a lot clearer a hundred years ago.
I think Prince Daniel has made a good job in his new 'career' of being a Royal, but I wonder how he feels, having only been made a prince because of his marriage to P Victoria. Women, e.g. Countess of Wessex, have no problems with 'stepping up' to becoming a princess, but I would imagine men might feel happier if they got a title based on their own merit. Women have been used to taking their husband's name/title for 100s of years; for men it's a new age.
Hope I made myself clear; I'm in two minds about the whole thing - and it shows!
You make an interesting point about women having no problem with moving up in rank by taking their husbands' title, while the reverse may feel embarassing or awkward for men.
Personally, my position is that there should be gender symmetry in courtesy titles for spouses. In other words, either both male and female consorts should be allowed to use their respective spouse's titles and styles, or neither of them should get any courtesy title at all, or both should get a different, gender-neutral title.
Spain uses mostly option # 1, e.g. the husband of a duchess is a duke with the same style of Excellency , and even the husband of the Princess of Asturias is called Prince of Asturias with the same style of Royal Highness. Husbands of infantas , under current rules, don't get the title (infante) and the style (Royal Highness) of their wives, but the same is true for wives of infantes, so symmetry is still preserved, albeit under option # 2. The only situation where there is gender asymmetry is the case of the husband of the (reigning) Queen of Spain, who, again under current rules, is just a prince and an HRH, whereas the wife of the King of Spain is a queen and an HM. Actually, that is a relatively recent innovation which was introduced in 1987. In the past, husbands of Spanish queens, e.g. Queen Isabella II's spouse, were called king and had the style of Majesty. The introduction of gender asymmetry in the titles of the monarch's consort in Spain seems to be a northern European influence (copying the British, Dutch, or Danish models).
Going back to your example about Prince Daniel, I would imagine that the position of "prince consort" to a reigning queen, as held by Prince Philip or by Prince Henrik in the past, and which will be most likely held by Daniel in the future, must be uncomfortable for most men. However, men who accept to take up that role probably understand (or should understand) what they are getting into and, in most cases, Prince Philip being the best example, they eventually come to accept the realities of their position and rank. Prince Daniel in particular seems to me to be quite comfortable with being "Victoria's help" and "walking behind her" metaphorically speaking. In fact, he said so many times.
In Jack's case, however, at least on this forum, we are not talking about his being made a prince in his own right, or even a courtesy prince (under gender symmetry). Both options would be out of question in British custom. The question here is Jack being made an earl (or a viscount, or a baron) in his own right in the peerage of the UK and being able to pass on that title to his firstborn son if any.
EDIT: BTW, just as a last comment, the idea of being made a prince "by merit" doesn't really make much sense (no disrespect intended) because hereditary monarchy, as shocking as it might be in our modern western thinking, is
not meritocratic. Men and women are
born princes or princesses and normally keep that dignity for life, whether they merit it or not. To be fair, however, as I stressed before, Prince Philip e.g. was only made a prince about
10 years after he got married, so I guess you could argue that he may have gotten that dignity "by merit" perhaps. He had been an HRH and a duke though since his wedding day, despite not being called a prince, which was very odd.