But I do think that there are a few Deacons who missed their calling to the priesthood and would have become priests if they were still single.
That is likely the case, and perhaps I am misreading what you are saying, but it does seem to imply that marriage and the call to priesthood are somehow incompatible. I suspect that there are some portion of men that may have never felt a calling to either the diaconate or priesthood if not for having been married and having children first.
Personally, I can think of maybe a half-dozen seasoned deacons that would continue discernment to the priesthood if their bishop asked them to. All of those men have living wives, and some still have children at home. One in particular had been ordained as a deacon in his late 30s and had been a deacon for almost 15 years before he ever felt a call to the priesthood.
I also know 2 or 3 priests that were married, raised kids, and then after their marriage broke down they petitioned for a declaration of nullity. I struggle to see a man that was ordained a deacon and then felt a call to the priesthood a decade later is somehow different to men who felt the call after their marriage broke down. I would say that they both could have valid calls and the only thing stopping one is the current discipline of the Church. I would not say either of them missed their calling.
Here really is my point. All people are first called to serve one another through the universal call of baptism. That call can further be strengthened via one or both of the sacraments of service (Holy Matrimony and Holy Orders).
Of the baptized, some men are called to a deeper service through the Church. Those men are ordained as deacons. Some deacons are then called to further service as priests, and some portion of priests are called to be bishops. It is a continuum and not separate branches as some often imply.
Essentially a priest must first have a diaconal calling just as a bishop has to first have a priestly calling. Neither are called to be a priest or bishop without those underlying callings. They might not directly acknowledge them, but diaconal ordination should never just be a check box a priest is doing as a step to the priesthood. That is part of the whole reason for the diaconte to be restored as a full and separate order. It wasn’t just so there was a level a man could stop at below the priesthood, but the recognition that it is not simply a ceremonial milestone. That separation does not mean that it is a completely separate path from additional consecrations in the hierarchy, but rather that each stage builds upon the earlier stage.
It is this idea that a permanent deacon has a different, and fixed, calling from a priest that I bristly at. I also think it is partially why there is the mistaken belief, as stated in the original question, that permanent deacons really aren’t part of the same sacrament of holy order.