that is absolutely untrue. i have built many "awesome" tanks that used standard shop lights for lighting, no co2 or co2 supplements, and no ferts whatsoever.
while the extra 6" of depth is nice, it's really not as much as you would think when you start building. you can definitely have a nice, 6ft layout and still have a sense of depth. it all depends on how you lay it out. here is my 125 before i needed to take it down.
and here is another of my paludariums which is 18" deep, but has a sense of depth to it. it's a 40b
ultimately, it comes down to what you can fit though. and just a suggestion, have you considered building a riparium, vs a paludarium? the frog would probably love it. here's an example of a riparium that a friend of mine built.
Duff's 2nd Riparium - Page 4
hope that helps