The difference is that Robin isn’t a series regular (yet, perhaps). He’s not required/expected to have any amount of screentime.
As far as Belle and her situation goes, I don’t know how much I trust the writers to deal with the consequences of Rumple’s lying over more than just an episode. Knowing them, it’ll be resolved in one episode and never brought up ever again.
And while she did have more screen time in S3B, what sort of time was it, really? She pops into scenes randomly to give information and exposition and then leaves again. Her time on screen may have increased, but I don’t know about the quality of that time.
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"He was a lot of things to me" "The only conclusion was love"