I don't think the +1 attack for mobs of 20+ boyz is that necessary. I mean big mob of boyz won't reach combat without taking casualties unless you have at least 6x30 or you succed a deepstriking charge (which usually ends up in overkill against screeners, so that many attacks weren't needed anyway).
The real strenght of 30 man mobs is its high amount of cheap wounds.
19 boyz plus a weirdboy with warpath in a BW can unleash lots of damage.
Talking about transports based lists, well that's my favorite way to play orks since 3rd edition

And I mostly play orks this way.
My favorite list, which is not the most effective one but
IMHO decent and fun to play, has 3 BWs, a morkanaut, 3 single skorchas, 4 meganobz with 3 or 4 pair of killsaws, 4
KMKs, biker mek with
KFF, biker boss and a weirdboy or warboss with killchoppa (they cost the same amount of points). 2x10 boyz in a wagon, 19 plus the footslogging character in another one, and meganobz plus 12 boyz in the third one. Sometimes I also include a trukk full of bustas, just cutting the meganobz and two skorchas.
The morkanaut is the bullet magnet that let the transport survive a little bit. I consider this naut way more effective than the gorkanaut because it has a worse profile but it's cheaper and already comes with a
KFF while if you want to field the naut you should also take a big mek with
KFF. The buggies add more armored wounds and may mess with some nasty deepstrikers, use them to let deepstrikers arrive where they won't be 100% effective against the naut or other expensive stuff.
I sometimes also play with just 1-2 BWs and more trukks or small units of kanz.