Can you measure the success of your leadership abilities?

My proudest moment as a Company Commander was at Hohenfels Germany at CMTC (now JMRC). I was commanding a Mechanized Infantry Company Team (2 Infantry platoons and one tank platoon). The tank platoon and my command track were taken out by indirect fire. My other two platoons kept moving towards the objective. The O/C actually let me get in his HMMWV and we followed one of the platoons who got in behind the enemy defenses. That meant more to me than other metric. When I rotated out of command, my PLs gave me a plaque with the Hohenfels map and the date this happened. It is one of my prized mementos from my career.

yes, daily

Producing another leader makes you a teacher, not a leader. Although, to be fair, a teacher is a leader. But, don't take my word for it. I'm a terrible leader. A reluctant leader. I find it sad that people need a leader. I find it even sadder when they try to follow me. Often, I have felt like the hapless hero from The Life of Brian... People seem to have lost the ability to lead themselves. It took me many years to understand the problem. People want a leader to take responsibility for their mistakes. They will surrender their individual liberties in exchange for freedom from responsibility. Interestingly, I discovered that was the primary role of a leader, to take responsibility. I was amused to learn in the Army that commissioned and warrant officers wore their rank upon their shoulders to signify that they could bear more responsibility. Enlisted officers wore their rank on their arms because they didn't need to carry as much. Well, once you leave the service you discover that civilians will follow anyone who shows any inclination to take responsibility.
https://www.youtube.com/watch?v=krb2OdQksMc

If the soldiers and NCOs rally behind me, I have done my job.

How do I know ... Is my mission accomplished and have I taken care of my Soldiers?
If yes then that's my answer. REF "the success of the people that you have led" that falls under me taking care of my Soldiers.

I judged my success on how well my units did when I wasn't there or if I declared myself a "casualty" and turned it over to my second or third or fourth.

As leader, I never taught classroom style, if the subject was MOS and mission related doctrine. I taught (or more likely, verified the knowledge level) of my 3-7 immediate subordinates, who taught their 3-7 immediate subordinates, who taught....ad infinitum.

Two layers down were expected to keep Marines usefully employed while 1st level was training. That way they exercised their leadership muscles. By the time Fire Team Leaders were teaching, the Marines had more proctors than they knew what to do with.

It sounds inefficient and takes a while to get it all put together, but it works. More is learned quicker when the student to teacher ratio is about 3:1 than when it is 30:1 or 40:1. No one gets left behind. No one can skylark. Strong leaders develop credibility with their subordinates quickly. Weak leaders show their deficiencies quickly. But you have to have a CO that is patient enough to get you through spool up. I was lucky I explained the process and got my CO's blessing.

Are your people successful? Are the progressing on a personal and professional level as a result of your mentorship and involvement? Are you confident they can take over for you in most (if not all) circumstances? Do they know you know this? You might be a leader.

There are tools you can use, such as a 360 assessment, that can help you identify your strengths and weaknesses as others see them, but regardless of the tools you use, the only person who can label you a leader is a follower.

For the most part, my companies could run without me unless we had tactical missions.

The best testament for me was when I was leaving I told a section head how good a job I thought he did and his reply was "I always wanted do do a little more for you."

The level of success of those you bring along. High percent of advancement among my people gave me the knowledge that I was doing the right thing acting as the example for the rest to follow intelligently and not blindly.