This is a right needle-in-haystack one
I looked at the 1841 census on FreeCEN, and there is only one David Ross of likely age listed as a clerk, aged 28, in Forres, not born in Moray. If his age is accurate he was born 1812/1813 and thus was at most 15 when Johan Fyfe's child was conceived about the end of 1827. In 1851 his age is given as 40 and his birthplace Edinburgh. In 1861 he is a writer (lawyer) aged 48, born Edinburgh.
I'm not sure if he also the 59-year-old shoemake, born Edinburgh, in Forres in 1871 with wife Jessie, 41, and a two-year-old daughter Jessie. However Jessie's birth (IGI) names her father as Rose, not Ross, as does the marriage index of her parents, so probably not.
Of course FreeCEN does not (yet) have full coverage of the census, so it may be that David Ross is lurking in one of the places not yet transcribed by the FreeCEN project. Though there is full coverage of all 33 Scottish counties in 1841, so if he is lurking as David Ross, it's not in Scotland.
Then again he might be lurking (or misrecorded or mistranscribed) as David Rose, or he might have adopted a totally different name.
I also looked at the online transcription of the Dundee Howff burials, but there is no David Ross described as printer, lithographer, clerk or writer there.
It is possible that Johan just invented a father for her child. She wouldn't be the first to do so, but in that event I'd expect her to have told the kirk session that he had gone to somewhere like America.
Odd that the extract came from the records of the United Presbyterian Church, which didn't exist in 1828 - it was founded in 1847. Perhaps it was actually the kirk session of one of the denominations that later amalgamated to form the United Presbyterian Church? However the absence of any mention of David Ross suggests that he was not a member of the UP congregation.
Perhaps he absconded in order to avoid having to maintain his child?
As for him being listed as deceased in 1856, this too may be a convenient bending of the truth, or maybe Johan had just told Alexander that his father was dead. These things happen.
There is a very small possibility that, if he was a member of some other congregation, that congregation's kirk session might have disciplined David. But you don't even know for certain that he lived in Dundee - it wasn't unusual for a girl to become pregnant while working away from home.
So I'm afraid I haven't done any damage at all to your brick wall. At best I have eliminated a couple of bricks that are not going to fall out of the wall.