That might have been a smarter play, although IIRC the surrounding territory was a big flat ball of suck. But since I usually discard El Dorado games for the purposes of posting, I had forgotten that buying a Settler was considered the best response.
Here's the prospective argument. Suppose you're pounding out 30
for 30 turns with the NC from turns 40-70, and you're setting up the Education slingshot. If you build Settlers instead of the NC, stunting your growth plus lacking the NC will cause that to crash down to an average of 14
per turn or so.
However, if you can add enough extra luxuries, you can simply pick up the lost
productivity through further RAs. Typically you'd sign three RAs on an Education beeline. Two extra luxuries for resale would let you sign two more RAs with funds to spare (assuming the AIs have the cash), which would actually improve your tech position when all of the RAs come in. You'd be able to get Theology and Compass with RAs and work on other techs after you finish blocking.
The ugly catch is that you have to secure those luxuries without provoking a DoW, or getting the extra luxuries is counterproductive. Pulling that off can be hard, but I suppose that it may be possible on some maps.