Yeah, that's what I thought. Eglinton appears busier. That's 80,000 per platform at Eglinton compared to only 75,000 per platform at St. George.
Seriously though ... the problem at Eglinton is that in morning rush, almost everyone is at the southbound platform, compared to St. George, where it is distributed more evenly.
In shear numbers yes. In terms of how crowded the platform is waiting for a southbound train? It's second only to Bloor-Yonge in my observations southbound. (northbound in PM peak though, Dundas seems the worst, with some others close behind).
I'd think Bloor platform at Bloor-Yonge, Eglinton, and St. George are all candidates for additional platforms at some point. Though I'm not sure how possible St. George would be.