In an effort to prevent the spread of misinformation, I present to you: Evidence.
Damage = (100 × Unmitigated Damage)/(Protections + 100)
So, let's pretend you have a full-build Rat with Titan's Bane, Jotunn's, and his 2 Maxed.
You're targeting a level 20 Ra with 60 base Protections. He's a complete noob, so he doesn't buy any Physical Protections.
A target's protection values can be reduced by penetration and reduction items. There are various ways of bypassing a target's protections. They are (in order):
Percent Reduction. This will reduce a target's protection values by a percentage. For example, The Executioner will reduce a target's physical protection by 8% (per stack).
Flat Reduction.. This will reduce a target's protection values by a specific amount. For example, Void Shield will reduce a target's physical protection by 20.
Percent Penetration. This will bypass a target's protection values by a percentage. For example, Obsidian Shard will bypass 33% of a target's magical protection.
Flat Penetration. This will bypass a target's protection values by a specific amount. For example, Dynasty Plate Helm will bypass 15 of a target's magical protection.
So, Rat's 2 is definitely considered Percent Reduction, so we'll start with that one.
60 - 24% = 46, rounded.
Then comes Titan's Bane's Percent based reduction.
46 - 33% = 31, rounded.
And Lastly, Flat Pen from Jotunn's.
31 - 10 = 21 after all items and effect applied.
So, overall, Titan's Bane gives you 40 power and an extra 15 penetration against this Ra, with no extra bonus passives. So, in conclusion, anything with more than 15 Penetration while still maintaining 40 Power (or more) will out damage Titan's Bane against squishies.
There are two items that fall into this range: Crusher and Brawler's Beatstick. Both would be preferable over Titan's Bane if your goal is to shred squishies in the most efficient way. However, Titan's Bane wins out by a LARGE amount when you tend to focus on more heavily built characters, or if the enemy has built substantial Protections against you.