Questions About KSing as a Jungler

I would like to get some opinions and fact checks on ksing when it comes to being a jungler. Let's say I'm Rek'Sai and that I've just pinged Fizz, my mid laner, that I am coming in for a gank. By the time I get in range of my Prey Seeker (burrowed Q), Fizz has already seen an opportunity to all in the poor Veigar who's already blown both his summoners. Fizz has ult, ignite, and rend all ticking away. Basically there is no way that Fizz isn't getting this kill regardless of whether or not I do anything. I'm pretty sure that in a scenario like this it's normally the right decision to fire a Q at Veigar in the hopes of getting an assist. Even if it steals the kill, landing the Q gets the team 50% more gold because there is a kill and an assist rather than just a kill.

Now let's apply a similar scenario to something like bot lane. There's an enemy Thresh and Vayne pushed up to our bot tower. I've just pinged that I'm coming in for a gank when Thresh lands a hook on our Leona and decides it's a good idea to activate it again and bring himself under tower. Vayne flash heal tumbles forward to help, but Thresh gets blown up by our Graves before she can land her first auto. Again, just as I get into range to fire my Prey Seeker at Vayne, Graves and Leona get her low enough that Graves ult and one auto will kill her. Assuming I have 100% faith in Graves landing his ult, I'm pretty sure in this case I shouldn't be firing any Qs. If I understand how assists work, the total amount of assist gold that the team can get is a static amount. Meaning if I were to land that Q, the ONLY two things I would be accomplishing is stealing some gold from Leona and potentially stealing the kill from Graves.

I know these examples were very specific, but I'm trying to capture the idea of the exact circumstances that I'm trying to look at. There are definitely a multitude of scenarios similar to the ones I've described in which I would be asking the same question. I also understand there are some very specific scenarios where it would always or never be OK to steal the kill. (Baron is up in 10 seconds and I'm 100g away from GA = always go for it, Baron is up in 10 seconds and Fizz is 300g away from GA = never steal it) Basically, I'm asking if my logic is generally correct in assessing whether I should or should not risk stealing a kill when it comes to a team perspective. Does this change at all when it comes to the kind of jungler I'm playing? (carry junglers, full tank junglers, support playstyle junglers, ect.) Is having 50% more gold on Fizz worth NOT having 100% on Rek'Sai? Is it actually somehow better for the team if i steal 25% from the support? What are the opinions on whether I should or should not be doing this in solo q when compared to ranked team games?

I'd also like to point out that I'm not talking about the kind of junglers who enjoy stealing kills. Sitting in a bush for 5 minutes as Kha'Zix and waiting for the enemy to get low so you can hop in and steal the kill is probably not ever a decision you made because you're looking out for the rest of your team.

There's also the risk of tilting the laner that you KS from if it's someone you don't know/trust. Is that enough of a factor to make it too much of a risk?

Not sure if there is necessarily a 100% guaranteed "right" answer to this problem, but I would appreciate hearing any thoughts or opinions that others might have on the matter. Thanks!