Yeah what Rellik and Chipla said, atm it's a bit too early to give any solid info or list advantages/disadvantage, simply because kingdoms only have plans and ideas, we can't say if infrastructure is good or not, we can't say how taxes work, the only thing that is semi solid atm are areas/tribes. and even then I would still wait for D&SS before listing it.
Also some things, like PvE/PvP, even taxes, that can't really be applied to whole kingdom, there can be PvE and PvP duchies within the kingdom, different counties may have high or low laxes. You can of course count the majority and establish the theme from there, but I think that would be incorrect, and generally a lot of domains will try to balance things out not going fully one way or another.
And lastly, if we will make some sort of review, it's the matter of who does it, kingdoms will rarely list disadvantages about themselves, and more likely to list bad things about other kingdoms, but a neutral party may simply lack info to give a proper analysis since their involvement with community will be limited and may not be long. So kingdoms may not be fairly represented, and get salty regardless in accusations are fair or not (remembering mickdudes post about all the kingdoms - people still got offended by some of his insights because his impression was not what they wanted)
P.S. I'm not against the idea itself tho, given time, more info and if someone want to do a proper research, it could be done, but probably not anytime soon.