I've got a question for you. Do you even math? Under what circumstances does 9% from 5000 gives you 4800? 9% * 5000 = 450 So the damage would be 4550, not 4800.
But let's have a more precise calculation. I've got 374 resilience on one of my 79 toons. This amount gives me:
4,27% less chance to be critically hit,
9,39% reduced critical damage and mana drain effects,
8,54% ADDITIONAL damage reduction from players and their pets
So having your example of 5000 dmg lava burst crit we got: 2500 (crit portion of lava burst, ele sham got 200% crit dmg, right?) * 90,61% = 2265,25
2500 + 2265,25 = 4765,25
Now we additionally reduce that amount by 8,54%, so: 4765,25 * 91,46% = 4358,3
Does that make a difference to you? Because to me yes, it does. It's around a 13% dmg reduction, more than warriors' defensive stance for example. Not to mention additional crit chance reduction, which vs shams lava burst will be useless, but still really good vs any other class which crit chance oscillates around 20-30%.
I also don't understand your logic with going to soft cap as a twink. Yes, you won't be able to reach cap as a twink. But what difference does it make? Getting cap doesn't magically makes you stronger. It's like a wall which stops you from stacking more of it. 20 more resilience gives you exactly the same value when you go from 200 to 220 an when you go from 1300 to 1320. I would even say that considering numbers only, resilience gives you more on 79 than it gives you on 80, because it decreases with level, like any other stat (crit rating, hit rating etc). But ofc it's just numbers, on 80 resilience is more valuable due to larger hp pools.
Let me also resolve your doubts about getting past 700 on 79. Without any item from coin shop you are able to exceed 800 resilience. With them, you can get over 1k (and I'm not exaggerating, I was making some healer build this exact morning and that's what I've created).
I'm not saying that resilience is better than stamina and period. Let's have an extreme situation. You have 1k hp, someone crits you for 2k. With 1k resilience he would hit you for 1170. Still an overkill, right? But with stamina, assuming that 2 resilience is worth 3 stamina (gem-wise) you would have 1,5k hp more. So after his crit you would be left with 500 hp. Not to mention that stamina is often increased (%) from talents. But the more hp-pool we consider, the more resilience becomes useful.
It's also worth to notice that healing abilities (not percentage of your total hp based) are more effective with resilience. A heal that heals you for 2k is more worth with resilience due to your damage reductions. It's harder for your opponents to again take that 2k hp from you when you got resilience. So for flag carrying with a healer on your back resilience is more preferable.
Anyway, I don't have a druid to test it myself and give an exact answer which would be better, resilience or stamina. Perhaps it's stamina, due to highly increased stamina in bear form. But on the other side, druid got a lot of non-percentage based heals, which would be more effective with resilience. Guess it depends on your playstyle. But still, saying that resilience is useless at lvl 79? That's just ignorance or lack of knowledge.
So I would lightly modify your statement: it's all about finding balance between damage, stamina AND resilience.
Resilience is useful at 79.