During monarchial times in Laos there were three kingdoms, including Luangprabang, Vientiane and Champassak. Champassak renounced claims to the throne for the sake of helping to create a united Lao within the French Indochina Union in 1946.
Although, I am not from southern Laos personally, I do argue in defence that Southerners are very much traditional Lao as those from the central and northern regions (namely Vientiane and Luangprabang), if not more so.
It is unfortunate that certain people insinuate that Southerners are perhaps subserviant to those from central Laos. But this should not be the case.
Southern Laos has an incredibly strong tradition of maintaining Lao culture. For example, it is often found that monks from the south are well versed in the Buddhist religious language of Pali while monks from the central and north are not as capable as their southern counterparts.
The south have food and cuisine that are distinct only to the south. To give just two examples, there is the southern style jaew bong which is heavy with padaek. And there is also the semi-hard, chewy toffee-like candy made from sugar cane. There are plenty more distinct dishes from this region which you will have to discover and experience yourself.
Southerners are also close followers of morlum music which is the traditional music of Laos. Morlum is incredibly popular in this region and many great musicians are from there.
I agree with your line of questioning that perhaps southern Laos is sometimes overlooked or not taken as seriously as being the real, true or traditional Lao - when in fact they are.
Info. Tidbits:
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Savannakhet (often simply referrred to as Savan) is the province with the largest population in Laos with over 700,000.
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Pakse, Champassak, is home of the Vat Phu ruins which is a UN World Heritage Site.
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Arguably, though not official, Southerners account for the largest proportion of migrants in Vientiane.
