so not true, there are plenty of subs that would do better sealed... it just depends on how the sub was designed, also clarify your definition of loud... a ported can be made so that 1 blows 3 out of the water, but to do so would usually mean you are burping it at a specific frequency... the box will peak highly at that frequency making the design VERY impractical for a daily listening system (because only a few frequencies will be much louder than the others)
so in my opinion, it largly depends on music preferance, if most of your songs have similar bass ranges, you should be great with a ported, but if (like me) your preferances include everything from rap to classical, sealed is most likely going to do you better, at the sacrafice of some volume...
again (in my opinion) technically the 2 ported have the potential to blow 4 sealed away but it's going to be hard to do it while mantaining a comparably flat responce and soud quality