I don't think it's realistic to make a calculator that adequately evaluates high-end rune beetles.
Every stat on a rune beetle is relevant for something that is at least somewhat important to at least one playstyle. There are so many stats available on a rune beetle that the odds of rolling a perfect one are pretty much impossible.
I personally rate beetles on 2 distinct sets of critieria. I'm either looking at a tanking beetle or a damage beetle. What I'm really looking for is a perfect beetle, though.
The most important thing for a tanking beetle is the total resists. The second most important thing is the HP cap on the beetle.
The most important things on a damage beetle are strength, dex/stam and eval int respectively. A beetle with high enough dex will swing very fast (swing cap) after it buffs itself.
I haven't found any convincing evidence that poisoning skill does much for you. It makes your beetle more likely to poison the target, but I haven't found that to be particularly important in pvm.
All of this is just my opinion, though. What makes a rune beetle good is highly debatable.
My advice to anyone farming beetles is to first look at the bard difficulty of the beetle. If it's < 112 before it buffs itself, don't even look at the rest. Bard difficulty is based on total stats and skills, so if you get one that's 112+, you know the stats and skills have potential to be good. The next thing I look at are the resists.
If the bug isn't pretty close to all the resist caps, I stop looking unless the bug is 114+ bard difficulty... If the bug has moderate resists and 114+ difficulty, I look at the stats carefully and decide if I want to claim the beetle as an attack beetle.
If you're planning to use an attack beetle, I highly recommend looking for a bake that's really high in HP/resists. I have found bakes to be the best 2 slotter for tanking.
I'll post if any changes are made to how RB's are rated!