I don't think this is true. I'm currently playing as the Dutch on a Monarch archipelago map and had marble in Amsterdam's BFC so I figured I'd go wonder-crazy. Well, right after I axe-rushed Huyana (I like placing a few extra civs to make things interesting).
Since I didn't have stone, I didn't go for the pyramids at all initially, instead taking the Oracle and Metal Casting as the free tech. The thing that makes representation so awesome in the early game is not just the +3
per specialist but also the +3 happiness. I figured that if I'm going to be relying mainly on 1 uber-city, I would need to lift my happiness cap early, so I went to Monarchy as soon as possible. Since I didn't have hunting, I was able to spam warriors for military police which allowed me to keep growing my capital very quickly. Note that I did have 4 cities at this point, 2 from Huyana, which made producing the warriors quite practical while allowing my capital to build other things.
As for wonders, I built the Oracle like I said and then the Temple Of Artemis, the Great Library and the Colossus in my capital and the Great Lighthouse in the former Incan capital. Combined with Financial, this has made for a very good economy on a water map and I'm getting about 900
per turn on a sustainable 80% rate at 1060 AD. Roughly half of that is from my capital and this is without Representation. Incidentally, I did get the pyramids later as I found stone on a nearby island but haven't changed to Representation until now as the +10 happiness in my capital from military police was more useful.
Anyway, my point is that while the extra beakers from Representation are very useful, Monarchy can be even better for raising the happiness cap of your capital. And higher population means that the science rate might not be slower at all if you have commerce tiles to work and your production is higher if you work hammer-heavy tiles. In any case, Constitution is not that far away if you want to beeline for it, especially if you burn a great scientist or two for lightbulbing in the Liberalism race.