I have never owned a Leader, but have had a Baker Batavia Special which was essentially the leader with steel barrels. I now have a Baker Black Beauty which is also the same gun with a different finish.
The Batavia line lacked what Baker called the draw bolt which absorbed some of the strain from the hinge pins & was not as highly ornamented as the Graded Bakers.
Even though over 100 years old both of mine have been tight & on the face.
I would not recommend one to someone who was planning on putting thousands of rounds through them a year, but for what sounds like your intended use it should serve your purpose very well. Prior to the Folsom buyout, the leader had been regularly furnished with twist barrels but Folsom resurrected it with steel barrels.
Whether or not an Ithaca Nitro Special is Stronger than a Baker Batavia is debatable. The Nitro special gained its reputation for strength in comparison with the Ithaca Flues. Most other American made guns already had amply strong frames, the Flues being somewhat of an exception. When the heavier loaded line of shells using the slower burning, so-called progressive powders, came out in the early 20's many of the Flues frames cracked, especially in the lighter weight guns, from too thin of sidewalls.
The Baker line did not have this problem.
I've never put a thousand rounds through anything and don't plan too(other than weapons with an "M" before the model numbers but that's been my job) the Grand American is held in Sparta 20 minutes from the house back home but Im not trying to take a hundred year old double in to a sea of Krieghoffs and Perazzis... My concern was, other than the is the gun safe to shoot question, is there anything that should make me shy away from this double for shooting some clays in the field or the one or two days of doves a year.