Yeah, pretty much. 

And so they would remain for more than three centuries, though the riverlords rose against Storm’s End at least once each generation. A dozen pretenders from as many houses would adopt the style of River King or King of the Trident and vow to throw off the yoke of the stormlanders. Some even succeeded…for a fortnight, a moon’s turn, even a year. But their thrones were built on mud and sand, and in the end a fresh host would march from Storm’s End to topple them and hang the men who’d presumed to sit upon them. Thus ended the brief inglorious reigns of Lucifer Justman (Lucifer the Liar), Marq Mudd (the Mad Bard), Lord Robert Vance, Lord Petyr Mallister, Lady Jeyne Nutt, the bastard king Ser Addam Rivers, the peasant king Pate of Fairmarket, and Ser Lymond Fisher, Knight of Oldstones, along with a dozen more…

As the ironborn moved up and down the rivers, reaving and raiding as they pleased, a bold young knight named Samwell Rivers, a natural son of Tommen Tully, Lord of Riverrun, assembled a small host and met King Harwyn on the Tumblestone, but his lines shattered…Lord Tully abandoned Riverrun without a fight, fleeing with all his strength to join the host gathering at Raventree Hall under Lady Agnes Blackwood and her sons. But when Lady Agnes advanced upon the ironborn, her belligerent neighbor Lord Lothar Bracken fell upon her rear with all his strength and put her men to flight.

…Many of the riverlords had joined the ironmen by then. Under the command of the Lords Goodbrook, Paege, and Vypren, they slipped across the Blackwater and fell upon the slowmoving baggage train before it reached the river, putting King Arrec’s rear guard to flight and seizing his supplies. Thus it was a stumbling, starving host of stormlanders who finally faced Harwyn Hardhand at Fairmarket, where Lothar Bracken, Theo Charlton, and a score of other riverlords had joined him.

House Durrandon had failed to establish any kind of legitimate claim to the Riverlands and clearly lacked any support aside from their Blackwood kin and a few other houses. By contrast, the Brackens had every reason to want a change of government – the Brackens had been loyal to the Teague Kings and wanted vengeance against the Blackwoods who had betrayed the Teagues to the Storm Kings. 

And clearly the Brackens weren’t alone – it’s quite likely that they were joined by other former Teague loyalists (and Seven worshippers) to fight a dynasty they viewed as foreign invaders.