There is no advantage whatsoever to being tall for the sake of being tall - if you can't leverage it, it's just a drain.
Well there's always some advantage, thanks to the scaler buildings like public school/museum/water mill. India's UA also makes population growth the only method to spread your religion. It's not like I was ignoring specialists either; I wasn't. I filled every possible slot as soon as they became available.
There wasn't much for me to do
except grow. I was placed on a floodplain with few hills to begin, so I grew. I suppose I could have used the UA as a means of being able to avoid growth, but that would hurt my religion, and doesn't seem like what India was built to do. Maybe I could have put some citizens as labourers, but my farms gave as much

/

as a labourer already, may as well get the food too.
None of this is very intuitive. The Harrappan reservoir gives +2

on farms, so I built farms to leverage that, and I got cathedrals to leverage that further. The UA gives religious pressure for higher pop, and removes my ability to spread otherwise, so growing is explicitly rewarded by the UA. With how it ends up screwing the happiness and luxury mechanics though, it feels a bit like a honey trap.
I'm not well-equipped to understand the formulas you have posted. Is this right for a simplified version of equation 1?
Happiness= (No.UniqueResources * baseHappiness) / (No.Cities/(FxTotalPopulation))
I have no idea what the "happinessPopulationDivisor.GC" is, so I can't really make heads or tails of that formula, other than to guess it is some product of a formula based on total population.
Even if that is the case, I don't think it's right that I am generating <25% of my gross happiness from luxuries (21/89). However the formula is working out, it's making luxuries fairly irrelevant.
EDIT: for funzies, I want to calculate the scalers I had on that city of 46

now:
Water Mill: 11.5

Factory: 11.5

Public School: 11.5

Museum (didn't have tech yet): 15

Stock Market (didn't have tech yet): 23

That's pretty cool!