As others have pointed out, the way in which you presented those numbers from a purely financial standpoint is misleading. However, the greater misrepresentation is that you fail to mention that the Gardiner carries a fraction of the people the TTC/GO does, in a manner which is polluting some some of the densest areas in Canada will stifling full development from taking off along the waterfront.it's far from bankrupting the city, don't be dramatic.
As large as the Gardiner capital program is, it's pennies compared to the capital spending the city is spending on transit. The Bloor-Yonge Capacity expansion alone is basically equal to the entire Gardiner capital program. The TTC 10-year capital plan is roughly 15 times the size of the Gardiner program.
The only reason the Gardiner is "50%" of the transportation budget is because of accounting purposes where most major transportation expenses are separated out, which is really mostly transit.