The original Romanceur was designed for off-road and dirt road light touring, and the original Lightning Bolt was designed for road riding. Sounds weird but that's how they described them at first. Of course, both the LB and Romanceur are good for both, but you'll see this in the original LB description that was on Crust's site that encouraged you to think of the LB as a road bike. The first mention of the Romanceur on Bene's instagram feed, "see what I'm cooking up with Crust", appeared over a year before the first Romanceurs were delivered about August 2016. That first instagram tease was followed by many many sightings of Bene's prototype Romanceur, and I would bet there was not a single photo of this proto Romanceur on or near pavement.
The key differences were that the Romanceur was built for wider tires while the original Lightning Bolt was built for Hetre/Baby Shoe Pass width tires. There was discussion at the time of delivery of the first Lightning Bolts as to whether they could fit Switch Back Hill tires or not, with fenders or not. This surprised many people since the Romanceur had lots of clearance for SBH plus fenders, and way more clearance between chainstays than required for Rat Trap Passes which was the tire Bene was saying was ideal for the Romanceur in his instagram posts. Since early fans of the Lightning Bolt saw it as a natural bike to run SBH, it seemed odd for fit to be questionable.
Some possible explanations for some of these things include that during these years (2015-2017) 650B listers and iBoBs were reading BQ and talking about a skinny tube revival and "under-built" 7-4-7 frames that planed. Meanwhile, before the collaboration with Bene, Crust had specialized in "over-built" adventure touring bikes. For example, the DNF/Evasion was their "light" adventure touring bike, OS tubing of course, designed not to break, clearance for Plus size knobbies, and for hanging an abusive amount of of Divide touring luggage on. Scapegoat was their less "light" adventure touring bike. When I read the original warning in the Romanceur description that it wasn't a touring bike but only for light touring, I thought what are they talking about--it looks ideal for a full touring load. Then when I got to know Crust's main offerings I realized, oh that's what they mean--if the DFL/Evasion is the lighter of their two touring bikes then they think of the Romanceur is a gossamer thing. Bene described himself at the time as a Riv fan whose Romanceur was inspired by the Atlantis with discs and low trail. But if you keep in mind that at the time, Bene's preference for a bike like a Riv Atlantis was quite a lightly built bike by Crust standards. (While on 650B and iBoB lists Riv's offerings are not considered lightly built even when they don't have extra frame tubes.) Meanwhile, Crust was adding frames like the Dreamer that were meant for road and designed for narrower tires. My point is that at the time, Crust was oriented toward touring being very different from road riding--touring was about Divide type riding and bikepacking. And by Crust's standards, Riv built lightweight bikes. That's why the Romanceur looked iffy for touring to Crust I suppose (and why their followup was the Nor-easter). And why the original Lightning Bolt looked like a road oriented bike to them with 42mm max tires. Meanwhile 650B listers just wanted to get the LB onto trails immediately.
It looks like Bene and Crust were also reading BQ and following Compass on insta- during this period and decided to try lighter tubing gauges for the LB and eventually try skinny tubes with light gauge on the canti-LB. A big departure from Crust's foundations which to me shows what an innovative little company Crust is and another example of how responsive Matt is. If Bene and Matt were slower to get on the planey light gauge bandwagon, it's only because 1) they were off living the effing good life on adventure tours rather than nerding out on BQ, 2) they were so used to OS tubing being so normal and required, so clearly the foundation of any bike you don't expect to break, that it may have taken a while for it to sink in "I guess they really want us to build a skinny tube bike?" and 3) they probably aren't crazy about dented down tubes from the front tire throwing pebbles up, and so had reasonable hesitations about 7-4-7 gauge tubing, skinny or OS, even heat-treated tubing.
To me, the Romanceur is every bit as versatile a bike as Bene imagined and developed, and probably more adept at heavy touring than Crust's conservative touring taste would indicate. (That's the first time somebody called Crust conservative, maybe.) The Lightning Bolt-disc is as versatile as the Romanceur, as long as it fits the tires you want. Both are super capable on road whatever the surface, and fun on light trails.
I ride a size large Romanceur and LB, and the canti-LB in skinny tubes is the only one of these three models that planes for me. Some people talk about how OS tubed bikes can plane if the gauge is light enough but I cannot tell any difference between OS 8-5-8 and OS 9-6-9 tubing gauge--both are beyond the threshold of planing for me. (My limited experience with OS 7-4-7 doesn't suggest it planes for me either). IME, I don't expect planing from any OS tubing bike, although it happens fairly reliably for me with skinny tubes in 8-5-8 and sometimes 9-6-9, even in typical 531DB and Columbus SL bikes. So as someone with experience of a lot of miles on a few of these Crust bikes, I suggest you not decide between the Romanceur and disc-LB based on planing because I cannot find a difference there. If you want a Crust to plane, get the canti-LB. Aside form looks (e.g. flllets v tigged v lugs) and tire clearance differences, the Romanceur and LB have very different sizing so find your best dimensions on their size charts. That's a good reality-based way of choosing between them. --Mitch in Utah