You would think that a tenor rebuild would be cheaper.I agree that a tenor is actually quicker than an alto. It is possible to get a greater range of suitable tools around the keys for tweaking alignment and making adjustments. Also bigger keys means easier leverage for bending, as HF suggests.
And Sopranos should be more then alto and tenor.Sopranos take longer because they re so fiddly. On an alto or tenor a simple bend may be carried out with a little pressure from a thumb. The same bend on a soprano may need special tools, and/or or removal of keys for access.