Completely uncomfortable. It virtually guarantees no championships in his era, unless the Cs draft or acquire a superstar scorer or big who becomes their cornerstone in the next couple of years.
Rondo's capable of playing like a superstar in the playoffs and leading his team to deep playoff runs. We've seen it in the past. You could say that some players are capable of better play, you could say some players are more consistent in dominating playoff games, and in both cases you'd be right. But we don't have players like LeBron or Durant on the team, and we don't have any realistic way to get one of them.
So, while I'd agree winning a title around Rondo is something of a longshot, I'd say there's little question that it's the most likely way we'd get one during his era. Look at the 2010 team that went to game 7 of the finals. KG wasn't healthy from his knee injury and PP and RA were clearly starting to age past the point where they could carry a team offensively. While those players were all-stars, none of them were on any all-nba teams, none of them were mvp candidates. PP was our best scorer, and he was tied for 20th in the league in scoring in the playoffs. KG was our best rebounder, and he was also tied for 20th in the playoffs in rebounding.
I think it's possible (although no small task) to surround Rondo with that level of talent over the next 4-5 years. Since you're so down on building around Rondo, I'd wonder whether you had a scenario in mind that you'd honestly say was clearly more likely to happen than that. No "we should just tank for a year and we'll end up with Wiggins" nonsense, something that you think is realistically likely to occur.