I don't buy into the Seven vs Kes debate. There was room for both characters, and if they needed to get rid of someone, Harry Kim was pretty useless.
Firstly, the character of Harry Kim would have been killed in S3 (1997) BUT his performer, Garrett Wang, was lucky to just be named, one of People Magazine's 50 most beautiful people in the world, and as one of the "20 Coolest Bachelors" in the country by E! Entertainment Television (what was a hell of reference, wasn't it?!

) at the same time.
Result: 1) Paramount felt forced to keep him to maintain the interest of its female audience (Mc Neil, Wang and Beltran) and ordered to producers, in particular Berman, to change their plans to get Harry Kim remaining aboard -> the producers obeyed in spite of Wang's evident lack of talent and his anti-professional atitude (numerous delays, no knowledge of his dialogues, undisciplined) on sets but
they have ensured not to give him what he wanted the most, a promotion for his character - who still was a simple Enseign after several years - and, some better stories ... though Wang, was better treated than Beltran, in this domain!); 2) because Wang/Kim stayed and it was necessarely to to free some place for the arrival of Jeri Ryan and her sexiness (even if the actress has proved talented -> I don't think that it could have worked on the long term if she had been worthless), the same producers - minus Jeri Taylor, the only female member, who was totally opposed to this idea - decided to fire Jennifer Lien, the actress who performed the role of Kes, because her character was considered as one of the less popular characters aboard according to a another poll (Harry Kim aka Wang was very closed behind!).
For my part, Lien, who was maybe not as talented as Ryan - but better than Wang and Beltran -, could have been kept somehow or other. I mean, maybe Nurse Kes was useless but a counselor hologram named Sek for example, would have been more interesting, especially with a Borg looking for getting her humanity back and a holo Doctor who too often showed his limits when it was a question of helping her...
In fact, it seems to me that the big problem was in the choices of the executives of Paramount, who have given priority to some secondary aspects like big names, glamour and sexiness, stupid polls, instead of getting talented and efficient people (from actors/actresses to scriptwriters). And on their side, Berman and Cie, were too shy to impose their will (the non-renewal of Wang and Beltran's contracts when it was possible, better scripts, etc....).
Secondly, about the relationship between Mulgrew and Ryan, yes, they were bad during the whole 4th season. I guess that the tension can be felt in their scenes though they managed to remain professional when they shooted. Afterward, they improved (we can see them chatting and laughing together between the scenes). Mulgrew apologised for her behaviour after to have explained her reasons and Ryan stopped to behave as a victim and to fuss for anything (we always talk about Mulgrew/Ryan's feud but don't forget that the rest of the team, though less outspoken, wasn't nicer to Ryan (I invite you to read some interviews given by Beltran, Picardo and Philips. Even Dawson recognized that it had been very hard for her to work with Ryan instead of Lien).... . In brief, big smiles in front of the audience in conventions when Ryan is present and behind, criticies at will!
Seriously, it would be interesting to see Mulgrew and Ryan working together again, 15 years later. Both are very talented and that they want to recognize it or not, there is a very good synergy/chemistry between them!
Thirdly, I was surprise and disappointed that Jeri Ryan, who was herself the complete opposite of a sexual character (contrary to the felt of viewers) and who showed so much potential during 4 seasons, accepted that her character of Seven of Nine ends as "a consolation prize of a tall blonde sexy wife" (dixit Picardo) for an older man. Sad.

