Danny Garcia lost to Spence by decision so that's probably the reason why he is crediting Spence a lot. It's like, he is still a force to reckon with because he lost to the best guy in the division. Though I seldom read nor hear any interviews from Danny Garcia and his twat dad, I did follow his career even before he became a world champion. He and especially his dad always feel they are the center of the boxing world.
The better way to listen to or read an analysis IMO is from Kell Brook and Shawn Porter as both fought Spence and Crawford. Timothy Bradley haven't faced Crawford and Spence but I do like his non biased analysis too. I'll bet all these 3 fighters will probably say Crawford is way way better than Spence if asked between the two.
These boxers refer to their own experience that's why their judgment is biased toward a specific boxer. It does make sense that they will have a view like that since they feel the strength of that boxer for real. About Danny Garcia's analysis that Spence is too strong for Crawford since he has experience fighting Spence, that's where his statement came from disregarding the other advantages that Crawford has.
I agree with you that a good analysis should come from a boxer that has experience fighting those who will be faced off. They can exactly determine the difference between those 2 boxers and their analysis is closed to being perfect and accurate.
Although in the end, no one knows what will be the final result.
Danny Garcia might say that Spence is better than Crawford, but I would believe more on Shawn Porter who faced both boxers and IIRC, Porter said that Crawford is the better fighter, so maybe if we listen to this guy, we will have a good basis and we will not be biased.