The first sentence sounds a bit odd to me, probably because failure and victory are words you tend not to encounter together, with one constrasting another. Not knowing the context makes it all the more difficult to understand what the message is you are trying to convey. You are not taking about a person here, obviously, because you used the word „this.“ THIS is more of a failure, etc. The word „failure“ is frequently matched with „success“ in English. „ The operation on the patient was a failure, unfortunately not a success.“ So English speakers are used to hearing failure and success contrasted with one another. Hence, „This is more of a failure than a success“ sounds more natural and expected to an English speaker`s ear. It`s the word pairing that makes it work. It´s like this in other languages too (German comes to mind) where certain word pairings are common, but not others. Failure contrasts with success (as opposites) but victory isn’t seen with failure, or at least it`s not paired with it to my knowledge. I think the second sentence is fine. The speaker is clearly NOT a doctor. No doctor would admit to „not being much of a doctor.“ The whole idea is simply not credible. You are either a doctor or you are not. But, some people do have some doctor-like skills (say a nurse or well-trained medical assistant). So, a nurse or medical assistant might say, „I`m not much of a doctor, but I can help you with those wounds.“ Even a layperson could say this. If a real doctor said he or she wasn’t much of a doctor, that`s a person I think I wouldn’t walk, but one I`d run away from.

Just one final quick remark. „Not much of an XZY (fill in the profession) does not mean „not a very/particulary good XYZ.“ Can you imagine getting on an airline and hearing „This is your Captain speaking. I`m not much of a pilot (not a very or particularly good pilot) but I think I can help you get to your destination.“ No one would say this for obvious reasons, because it implies the person is not competent. But, if you were say on a small plane, and the pilot had a heart attack in flight and died, a passenger with a few hours pilot training, without a pilot`s license, might say „I`m not much of a pilot, and have only had a few lessons, but I think I can land this thing safely.“ Now, that works and is credible.

More is usually used as a comparison Much is usually used for uncountable things. I know more of the English language than you. Comparison You won't know how much of the Portuguese language I know until you talk to me. Uncountable Using the preposition of after more or much makes it more particular than general He doesn't know much English He doesn't know much of the English language You know more Portuguese than me. You know more of the Portuguese Language than me. I have also illustrated their use in my reply below This is not much of an explanation it's more of a complaint. I would never let a doctor who spoke like that treat my wounds. I would say he is not much of a doctor don't let him treat your wounds. I hardly think a doctor would talk about himself like that he would be more of an egoist and declare how good he is. Hope that helps you Luiz

The correct way to say the second sentence is: I am not much of a doctor, but I may be able to help you treat those wounds. The phrase you are querying is actually 'not much of', which means 'not a very good/particularly good' doctor. One would never use the words 'much of' in this context without the word 'not'. In the first sentence the phrase 'more of' or just 'more' on its own is used when two qualities are being compared. One could also say: I am more a failure than a success (victory is not the correct word here, as one would not describe oneself as a victory, but rather as a victor, a victory being something one can achieve, but not be).