It depends on where you're drawing our line at for sub-Ω builds. For a .3Ω, yes, you will have more power in a mech than with either the DNA30 or the (current) SX350. To say that a mech is safer is just wrong. There are NO safety features in a mech except for (sometimes) a collapsible spring. These boards have safety features which will prevent a catastrophic breakdown from a short or if you exceed amperage overhead.
If you're talking a .6Ω build (still well within the sub-Ω category), you couldn't be more wrong about the power.
Even with a FULLY charged battery on a mech with 0 voltage drop under load (which isn't possible) you're only vaping at 29.4W. The DNA30 will get you the full 30W, and a (current) SX350 will get you to 35W. And with these chips you will get that power for the life of the battery, not however long your battery is at full charge (which isn't very long).
There is an upgrade in the works from YiHi for the SX350 which will bring it to 40W very soon, and eventually 50W. You can get that from a mech with .3Ω, but only with a mech that will put out above 4v under load.