My understanding is that tapered leaders are made by taking (just say) mono of .019" heating it and stretching it to the smaller dia. So I would expect that it would be weaker than mono which was not abused in this way.
However, at our club last year we discusse and created leaders. Regardless of how much a knot degrades strength, the weakest point in the system will be either the knot on the fly or the knot where the tippet attaches to the leader.
We used a Loomis rod attached to a fish-weighin scale and applies enough pressure to double the rod. The scale measure 2# of pressure. It is the sudden snap of pressure that breaks tippets, not constant smooth pressure. So I agree, the weakness of the tapered leader is not a problem unless the line is jerked sharply.