Yes, I am sure that a 14 inch tenon saw will cut much faster than a short dovetail saw when using full strokes. And I suppose that can make mistakes happen very fast. On the other hand, in my limited experience, and at least up to a point, I have found the faster cutting saw far more accurate than the slower cutting saw — though I doubt my Lie Nielsen cuts as fast as Ed’s saw. After struggling with cutting dovetails and tenons accurately, I found three things that helped a lot, a sort of trifecta of discoveries. First, a more aggressively sharpened, faster cutting saw. As Ed mentions, all those extra strokes of a slower cutting saw seem to increase the chances for messing up, or even to guarantee messing up, I at least in my case. Second, trying to control the way my hand naturally wants to twist in each stroke of the saw. Oddly, my hand wants to twist in different direction on either side of the dovetail. Third, I made a Moxon vise which raises the wood to a more comfortable height for dovetails. (Has anyone else found that planning, cutting dovetails, mortising, etc., all seem to want different height benches?)
Anyway, just a few thought from someone who still finds it amazing that my own hand cut dovetails actually come together pretty well most of the time.