How do you use a lead to end the game on Twisted Treeline?

I've only just started playing twisted treeline. In my 5 games so far: First game we got stomped, everyone lost like 17 kills to 5 (I was 2/7/2). Second game, my jungler ragequit after starting 0/3/0 because my top laner was a bot that ended up 0/17/0. I went 4/5/0 getting all 4 kills in 1v3s. Nonetheless they eventually ended 3v1 (the bot wouldn't surrender with me). Third game we won in a stomp, 19 kills to 3.

Now the 4th and 5th games are the ones I'm asking about. In both cases I was playing J4 jungle against Kayn jungle (and the enemy team had a Malzahar both games). Game 4: At the 10min mark we had a 1k gold lead, and it was slowly but steadily growing to a 4k gold lead at 33min, when they surrendered. We had just won another close fight (3 for 2) and our teemo would get the first inhib of the game for us had they not surrendered. Even though we had all the map pressure and were winning fights, it was so hard to get anything off of anything. We'd either trade 2 for 2 or 2 for 1 or 3 for 2, and whoever was alive would be so low they couldn't push any objectives after. I thought TT would be a faster mode, but 33min to get the first inhib is slower than most games on the rift! Had they not surrendered, I feel like that game could have gone to 50+ minutes. I finished 11/7/9. I feel like we probably could have stomped harder, but since I started 5/0/4 I went with a really greedy build which gave me no defense and let their malzahar ult me every fight. Even though I ended up getting QSS I'd still typically die to all the focus damage (but it did let my allies clean up). Had I went with my normal J4 build (i.e. tankier, like in game 5) I think we probably could have won teamfights more convincingly.

Game 5: Another game where I got off to an insane start, 3/0/4 and 3/1/6. This time I went with a tankier build though. Yet again, while we were winning fights we were never winning convincingly enough to take Vilemaw off of it or anything. Our gold lead was 1k at 7min and ended up at 3.7k at 20min when they surrendered. We didn't even have an inhibitor turret yet, and I don't think it was very likely we would soon (their strongest champion Pyke had just been solo killed by our Akali who was low, the other 4 of us all full). I finished 5/2/9 and the tankier build was definitely better as Kayn, Pyke, and Malzahar were still focusing me but I was surviving this time. I felt more like we could have ended this game because we had a Vayne who seemed to be hitting her stride, but again didn't get the chance.

So, given those experiences, I've had a couple really good, close, fun TT games. However I've never really seen a game end through a team actually ending. It's always a surrender or a stomp. So how do you end? Is it really just a matter of not making mistakes and getting a super long ace out of them at 40+ min? That doesn't seem right for a smaller map that you expect to end faster. Perhaps it's safer to take vilemaw? However when I tried in the game 3 stomp we were easily stopped each time, it simply took too long to kill and did too much damage (my only deaths in that game came off of me trying to kill vilemaw - albeit despite pings my team didn't help so I was soloing it).