Shields can ignore a very high percentage of damage with a low equipment cost, since shield resistance is based primarily on your shield power level but also your bridge officer abilities. The same abilities that restore your shields also usually "harden" them so they take less damage. Hence the massive and enduring popularity of Emergency Power to Shields and Transfer Shield Strength. Gaining significant hull damage resistance requires that you have and spend a whole bunch of engineering consoles while gaining significant shield damage resistance is about jacking up your shield power level and knowing when to use shield hardening abilities.
For non-resilient shields, 10% of the incoming damage is going to leak through your shields no matter what. It's very easy to have your hull melted to slag while your shields are still strong and all your shield-related abilities are working at maximum efficiency. That is why you should have at least some armor and some hull healing. Resilient shields only leak 5% of the incoming damage, which is basically the same as gaining 50% immunity to all damage through armor as far as the bleed damage is concerned. Though Resilient shields tend to have other drawbacks, like a lowered capacity or lowered recharge rate.
I will second the notion that the engineering consoles that boost shield power level are a very very poor "value" and should generally be avoided. Pretty much all the power boost consoles are very inefficient use of slots.