Not that at all. More about value. You add a nice 3rd guy and you would have the trade weight to get anything. Sale cost little more than what the Cubs gave up. And honestly looking at it today the pieces are trending better.
You're assuming that trade was available when there were specific reports at the time that the sox wouldn't deal sale in town. That's the problem with hindsight analysis. People always assume the trade was there for your team. I think it's more likely the market for Q dried up giving his pitching style(he was never a high k rate guy) and the fact that he was having a poor start to the year. That mattered less to the cubs because A) he pitched like a cubs pitcher when he was good and B) the cubs didn't have a ton of options. Ultimately there's a reason players get traded. If they are on the market to begin with you're almost certainly going to have warts. Sonny Gray was traded at the same time and look where he is right now.
I think people also are overreacting on what they lost. Eloy is a good hitter but he's a pure LF. In other words, if he's not a better pro hitter than Schwarber it's a very moot point because his bat has to carry his overall profile. I'm not trying to undersell his bat either but if he's just a 130 wRC+ as a LF he's not really that big of a deal. For example, say he's Nelson Cruz. Cruz is a career 130 wRC+ hitter. He's a good hitter but has he ever truly been the guy you build a team around? He needs to be more Aaron Judge or JD Martinez. As SlienceS said, Cease is the bigger loss in my eyes. But there's enough issues with his walk rate that it worries me he may never reach his ceiling. He's never had a walk rate under 3.5 per 9 at any level. He has all the stuff he needs but you don't reach ace level with 3.5 bb/9.
Regardless, I honestly think it's a wasted point to bring this trade up. Unless Cease ends up a #1 or #2 starter the cubs have more than enough interesting arms who can be #3-5 starters. And as for Eloy they have either the #1 or #2 offense already in baseball depending on how you measure it. There is of course the argument to be made that other trades may have been out there but I'd counter with who? The pirates weren't trading Cole in division. Gray hasn't worked out either. Sale if you can show me where it was an actual possibility would make sense but the reporting was the sox wouldn't move him unless they got bryant which is a "**** off" offer. Cubs clearly talked to tampa about Archer at multiple points.
And I think it's worth pointing out Q could just as easily find his groove again this offseason. I mean look how shitty people thought Heyward was. Q isn't *that* bad. If he regains his form this offseason you still got him really cheap for 2 more years.