Costa definitely came in shape, but he's never developed elite skillsets in any area. In some way he reminds me of Travis Browne, who had the athleticism and raw material to be a better version of Tim Sylvia. But while Sylvia developed a good jab and effective striking game using his height/reach, Browne was never more than a moderately well-rounded brawler. That's pretty much how I'd describe Costa, too.
Costa did well against Romero because Yoel had the same limitations. Great, explosive athlete with a lot of power and strong chin, but didn't put together combos well or have a gameplan to beat another elite fighter besides a flying knee or superman punch KO.
DDP is interesting because he has some similarities with Costa and Yoel but finds ways to beat really good fighters like Whittaker and Strickland. I think his awkward/unorthodox style and ability to follow a gameplan (even when it doesn't seem to be working well) sets him apart from the others.