How strong the Supreme Kai really is?/How strong is Buu Arc Piccolo? Why it is believed he surpassed the Cell Jr?

[dragonball0900]

The Boo Arc has a ton of ridiculous implications, but there's really no reason not to go with the Base Saiyans > Piccolo. Yes, it causes a lot of bloating in the Cell Arc, and we all don't like it in general, but they're all far too clear to ignore.

Yeah. It seems more like a small retcon. In the Buu arc, the base saiyans are portrayed as stronger than Piccolo, and the SSJ is portrayed as a small boost (see the Yakon vs Goku kilis numbers, as well as Base Goku vs Yakon and you'll see what I mean). Later in Battle of Gods, the 50 multiplier returns back, with the base saiyans weaker than Frieza, like it should've been.
I recommend using a 2.5 multiplier for the Buu arc, to make things having more sense. There's also Base Gotenks, which many people, included myself, get confused how strong he really is. The only way to find it out is to use a smaller multiplier in the Buu arc so that everything makes sense, then in Battle of Gods and beyond the 50 multiplier should be used.

[Grimlock]

Dabra, who was rivaling Gohan in strength, is also said to be as strong as Cell, and Cell was as strong as SS2 Gohan before his death.

We don't know if the comparison was related to Perfect Cell or Super Saiyan 2 Cell. Goku was dead and Gohan and Super Saiyan 2 Cell never fought, they launched their Kamehameha as soon as Cell returned. Unless the guides specifically states something that I missed.

[Analytic]

but there's really no reason not to go with the Base Saiyans > Piccolo.

Goten being comparable to Gohan in strength but not being able to overwhelm #18 in base form is a good enough reason if you ask me.