I shall avoid the issues of acting ability and monetary concerns as I feel enough has been said on these in 16 pages!
My major issue with the change form Jadzia to Ezri is that, once again, the position of Science Officer (in terms of a senior officer who is a regular character) disappeared. Granted that it was written in a time of war and so a Counselor was needed to asses the psychological state of the crew, however this seems to have become the norm in post TOS trek.
TOS - Spock > Sonak (TMP, killed in transporter accident), Decker > Spock.
TNG - Apparently Data, amongst everything else he did, but he is an android, so I can not argue. The only additional point is the existence of dedicated science stations on the bridge, but no "perma-character" to use them.
DS9 - Jadzia Dax.
VOY - Mix and match until "7 of 9".
Ent - T'Pol, however this just, in my opinion, felt like fan service ~ a Vulcan Science Officer, where have I heard that one before? As well as "eye candy" ~ a female in skin tight cat suits, once again, where have I heard that one before?
It just seems odd to me that a role with such a high level of importance, in a show about discovery and exploration, keeps disappearing or being incorporated into other roles.
I am not sure what you are getting at. Dax is the only case in which the character disappeared and there was not science/ops officer. And, yes, Spock would not have reprised his role in the anticipated Next Phase series, leading to Sonak being created. However, those changes were made largely due to the choices of the actors, not because of story choices.
Perhaps more importantly, Deep Space Nine is not about "exploration and discovery." It is about encounters and conflicts. The science of of Trek was deliberately weaker in DS9 than in the other series of the franchise. Dax, along with Bashir and O'Brien, were there to inform us about science and technology issues when they were relevant. However, her character was more important as the Old Man: the person who advised Sisko about political and strategic issues.
It is worth saying that Enterprise was only secondarily about exploration and discovery: it was primarily an origins story of the other series.
Sorry, I was being a pedant with regard to the non-existence of the role. My working role is within the Sciences and consequently I deem it to be a high priority division, especially when no other Officer possesses this as their primary specialism.
Furthermore, with O'Brien being the Chief Engineer and Bashir the CMO, they would more than likely be busy within their respective roles, particularly in a combat scenario. As such, if a new ship/ weapon/ similar were to come to bear upon the Defiant, the Science officer would be the logical person to analyse and apply/ recommend a method of countering the new threat.
Hopefully this clarifies my thinking more coherently than my previous post.
