I agree that playing "your pet deck" helps to win, mostly because you have the most experience with. I doubt that playing "your cards" is helpful as the card does what it does, certainly in regards to the deck strategy/design.
For me: I will most probably be more successful on tournaments if I would play Bant all the time, but an old pet card like Stonecloaker will most probably lower the power level of the deck and is not the best choice. I can also write heroic stories what Stonecloaker did for me in the past but in the end the card is to borderline to be a staple. Certainly if you have a meta full of Reanimators he will be set again.
Another aspect is that pet decks tend to disregard basis rules of successul deck design. Playing GG/UU/WW in Bant is obsolete IMO with the new mulligan and should be reduced to UGw or GWu. Having Courser, Counterspell and Hero of Bladehold in the same deck might look like a good idea for "your pet deck" on paper but is not the best idea if you want to have the best Bant tournament deck as you will very often not be able to play Counter/Courser/Hero in T2-4.
For me: I will most probably be more successful on tournaments if I would play Bant all the time, but an old pet card like Stonecloaker will most probably lower the power level of the deck and is not the best choice. I can also write heroic stories what Stonecloaker did for me in the past but in the end the card is to borderline to be a staple. Certainly if you have a meta full of Reanimators he will be set again.
Another aspect is that pet decks tend to disregard basis rules of successul deck design. Playing GG/UU/WW in Bant is obsolete IMO with the new mulligan and should be reduced to UGw or GWu. Having Courser, Counterspell and Hero of Bladehold in the same deck might look like a good idea for "your pet deck" on paper but is not the best idea if you want to have the best Bant tournament deck as you will very often not be able to play Counter/Courser/Hero in T2-4.