we know they had ship to ship communications.. the treaty was done with subspace radio.. even though a later episode of tos sorta contradicts this..

really a lot of tos wasnt pinned down yet in the early episodes.
the trek universe was rapidly evolving during tos and has issues all through it.
some thoughts..
the romulans had to ftl travel the issue that scotty bought up was the power source.
it may be they just didnt understand the full true nature of it.
but not only would the romulans need ftl to rule over a vast
empire they wouldnt been able to get to the different outposts so fast without ftl.
spocks issue with invisibility was the power drain.
indeed after minefield we never do see an invisible cloaked ship.
during minefield they indeed seemed to be have issues with the cloak.
remember the ships seemed to cloak and decloak with out rhyme or reason.
if the romulans in minefield where testing the system and couldnt get it to work helps explain why they went to the holographic system.
which of course was useful to sow distrust.
but it makes sense if news of an invisible cloak would have been deep secreted.. can you imagine the impact on the civilian fleets if word got out.
and since a cloaked ship never was seen again less chance of the knowledge getting further out.
i do have issues with the whole never seen a romulan.
bodies get sucked out into space during battles.
so either they did use drone ships or bodies were seen but due to politics a decision was made to keep this information secret.
and there is no reason visual communication didnt exist between ships.
the way it works in enterprises time is that you cant get visual on the other ship unless they allow you to.ie turn on their visual along with audio communications.
unlike in tos where you can track back a communication signal and see into their bridge without their knowing about it.
and sorry the nx is pretty damn primitive as compared to the tos enterpise.
something that got establised in the mirror episodes..
the other ships were puny nothings compared against the defiant.
and that was with a crew who were just starting to learn how to operate her.

really a lot of tos wasnt pinned down yet in the early episodes.
the trek universe was rapidly evolving during tos and has issues all through it.
some thoughts..
the romulans had to ftl travel the issue that scotty bought up was the power source.
it may be they just didnt understand the full true nature of it.
but not only would the romulans need ftl to rule over a vast
empire they wouldnt been able to get to the different outposts so fast without ftl.
spocks issue with invisibility was the power drain.
indeed after minefield we never do see an invisible cloaked ship.
during minefield they indeed seemed to be have issues with the cloak.
remember the ships seemed to cloak and decloak with out rhyme or reason.
if the romulans in minefield where testing the system and couldnt get it to work helps explain why they went to the holographic system.
which of course was useful to sow distrust.
but it makes sense if news of an invisible cloak would have been deep secreted.. can you imagine the impact on the civilian fleets if word got out.
and since a cloaked ship never was seen again less chance of the knowledge getting further out.
i do have issues with the whole never seen a romulan.
bodies get sucked out into space during battles.
so either they did use drone ships or bodies were seen but due to politics a decision was made to keep this information secret.
and there is no reason visual communication didnt exist between ships.
the way it works in enterprises time is that you cant get visual on the other ship unless they allow you to.ie turn on their visual along with audio communications.
unlike in tos where you can track back a communication signal and see into their bridge without their knowing about it.
and sorry the nx is pretty damn primitive as compared to the tos enterpise.
something that got establised in the mirror episodes..
the other ships were puny nothings compared against the defiant.
and that was with a crew who were just starting to learn how to operate her.