I am amused that we have soberly and sensibly come to a sound doctrinal reason for the hilarious Miranda spam of the Dominion War.
Also, I've got a couple of reasons why I think the Cardassians are backing reformers in the Bajoran system and not the entrenched establishment:
1) Bajorans have been isolationist for centuries if not millenia by this point. The establishment almost certainly thinks that alliance and affiliation with /any/ alien power is unnecessary and perhaps even heretical at this point.
2) Even the Cardassians don't think of themselves as the bad guys or oppressors. They often are, but as is the way of such things they obviously have good reasons. The Cardassians seem to view themselves as hard nosed pragmatists making the hard calls. Upsetting an ancient and stagnant hierarchy to increase efficiency could well be part of that. They simply don't see any value in a caste system that would tell them "we simply cannot increase our ore quotas because we don't have that many miners and they don't increase in number". There may also be a practical reason for adopting the reformers side: it gives them a ready made pool of dedicated and enthusiastic collaborators working for the "common good". (As they seemed to have right up to the end in canon)
3) As a consequence of 1 and 2 the Cardassians most likely contacts are with the reform minded as the people in charge won't give them more than the time of day. I suspect our own contacts were better recieved by the establishment specifically as a counterweight to growing Cardassian backed calls for reform. Otherwise they would have told us to fuck off too as there is some evidence that their caste system is more entrenched than the /Apiatan's/ (The Apiatan are not as worried about the possibility of it going away one day as it is biological in origin rather than theological)
4) EU sources tend to lean towards that interpretation IIRC.
5) The official line is that the caste system withered away due to the needs of the resistance. This is unlikely to happen unless the caste system proved that it was not up to the task as a people as universally... fanatical as the Bajorans would not give up on such a tradition easily (Witness how readily they tried to read readopt it when they thought such was the will of the "True" emissary) This implies that the caste system fought the Cardassians and lost. Incidentally, this is why I suspect that the first phase of the resistance will be fanatically religious in character for a couple decades until a generation or two watches the caste heir achy smash itself to bits and failing against the Cardassians.
I think the Cardassians being pro-reformist is most likely, for the reasons you have listed.
Considering this I beleive there were probably three stages to the occupation.
The first stage would be the Cardassian assisted coup by pro reform theocrats within the Bajoran government. They would have mostly seen the Cardassians as useful tools with which to achieve their own aims. Their goals aren't that radical, and they aim to continue on mostly as before, only with them in power, and a few necessary reforms.
They may even have believed that accepting Cardassian suzreignty was the only way to ensure the isolation of Bajoran culture from foreign influences (eg. the awful immoral hedonistic Federation.) This first stage will likely be the shortest, maybe lasting as little as five years.
The second stage would have occurred as the moderate reformism of the coupists would have come up against the Cardassian's own ideas of what Bajoran society should be. This may have been a gradual transition or a quick one, but Cardassian soft, and later hard power would have been irrefutable. The Theocrats would have been pushed out and replaced by a secularist utilitarian, puppet government with a modernising agenda.
This is when the resistance would have got serious and would have definitely had a religious bent. The caste system would have rapidly dissapeared and resource extraction would have dramatically increased. However there still would nominally have been a Bajoran government.
In the third and final stage we see the Occupation described in DS9 begin to take shape. The collaborationist puppet government would have tried its best to fulfill Cardassian demands in the face of rising resistance and probably struggled on until the 2440s. However then increasing violence on Bajor, leading to a decrease in productivity would have coincided with severe resource shortages throughout the Cardassian Union. The Cardassians would have taken a hard line, and eventually either an event is manufactured or a real incident is used as an excuse to portray the puppet government as incompetent and justify a direct occupation under a Cardassian lead administration.
This would be the same era that featured agressive Cardassian resource hungry expansionism that lead them into conflict with the Federation.
On Bajor the previously religious opposition was probably mostly under control by Bajoran internal troops, and Cardassian military aid, likely reduced to one or two big showy terrorist attacks a year. The direct occupation would have reinvigorated it, with a massive influx of previously moderate Bajorans who had until now tolerated the 'hands-off' Cardassian interference of the previous era.
The last vestiges of the caste system would have slipped away as every recruit to the resistance was needed to fight the hated invaders.
Collaborators would still have been pretty common in the early days of direct occupation, but gradually the Cardssians would have come to see them as unrelaible, not without some cause. (Posing as collaborators is a good way for the resistance to inflitrate them.) Tme military effort would have become almsot totally Cardassianized, and almost all major positions are filled with Cardassians. This would have further alienated the few pro-Cardassian Bajorans left, bolstering the insurgency.
This is the era Kira Nerys grew up in, as the Cardassians grow ever harsher in their demand for more resources, and in the face of increasingly fanatical Bajoran resistance. The stalemate against the Federation in the war likely only made things worse for the Bajorans. As they are forced to garrison Bajor with ever more trops the Cardassians become increasingly brutal, leading to the excesses we are told of during DS9.
What we end up with is very much a the paradigm of the harder the Cardassians tigtned their grip, the more that slipped though their grasp. Until eventually Bajor became such a burden upon them that they are forced to end the occupation, and cast it loose. (Increasing Federation pressure, alarmed at the plight of the Bajorans, would have likely influenced this as well.)