Yes, a single source is most consistent. And a good reviewer should separate observation/objective and interpretation/bias.
The reviewer should first describe the sound, then judge it according to their liking. A quality ranking should be independent of taste.
In the end, we rank the reviewers...obviously Whathifi is not the most credible for me. I particularly like one who gives extremely detailed reviews that let you read between the lines.
There are some reviewers who are telling us right away that they judge earphones according to their personal tastes only. Such reviews are only informative when you know their tastes.
Worst reviewer of all that begin to fall on my nerve is the Phonograph....going into his blog its like going to brothel but instead of girls its publicity...all look like copy paste description find somewhere else. I always fall on him when I google a chifi iem these days...second worst one is ''Bad guy good audio'' from youtube, he's an headfier too, don't remember the name, but hes the master to talk and say nothing about DAP and again I always fall on him on youtube especially when trying to get factual info about Opus 1 DAP....video was 20 minutes long and he just talk about his life and the DAP look.
For the good ones, I like B9scrambler review but unfortunately he don't like to give score on his blog (on headfi he do it no choice!), as I like both: good explaination AND score it sometime make me confuse to know if he really like an IEM or not, but when its too minimalist like with Audiobudget or Vidal, it can lack in description, tough the graphic with score of Vidal is very wise and informative by its own. All in all, review are a plus, but making conclusion on it still is risky, I read SO MUCH reviews....different one to compare and make my own conclusion, and asking questions here, in fact, all in all, its on headfi that I find the more valuable info, I really like it when there more than 2 reviews so I can compare. I like it when there debate about soundsignature advantage too, good or bad. I feel a reviewer must have wide music taste too, so he can really test the gear properly, if he just listen to one type of music review will be half done at best IMO
About sound source, I feel in the contrary that it need more than one because it colore the sound, I really don't give lot of credit to reviewer that only use a smartphone for example, 2 DAP, a neutral and a little colored, even if I do not beleive in plain neutral DAP cause just the power it push can inflict on IEM sound.
I just finish the review of my Xduoo nano D3 and it was quite hard....make sometime I did not review a DAP, and english writing really fock my brain sometime especially to be precise about sound description or some fancy terminology....but the secret I say at they end is true, I really think I prefer his sound to the Xduoo X10! For my next reviews I think I will create a playlist with ALL music style possible. Need some discipline really....big problem with that!
And your right, WhaThiFi is What in must case...I was reading this before falling in headfi hehe