It was a circumstantial game, ofc I do those things when I need to, the key words being "need to". Our team was losing rather badly, and I carried them back, we had good vision, and as you said Reng has rather strong dueling powers as it is, I didn't need to sink the extra gold into a jg item.
Ofc you wouldn't know, because you didn't think of the build, but the whole idea was to focus around ult, that's what makes the Dead Mans so viable on him being able to jump in and focus your momentum into one deadly burst eliminating the biggest threat, and then having the survivability to finish off whovers left standing.
And yes, I know the mechanics of jungling, thats where I spend 80% of my play time, I kind of pride myself on being able to get first blood almost every match because I know, when to ward, where to ward, and when to fight. Anyone has the ability to be strong against other junglers, some just have to be wiser than others.