The premise here is great - it's of course *preferable* to draft your QB vs acquire him through trades all things being equal. The cost for the player is lower in most measurable ways and probably in most situations (not a GM, and I don't play Madden).
However just listing out SB winning QBs and whether they were drafted by that team is information missing a lot of meaningful context: how often do franchise / superstar/ [pick your descriptor] QBs come on the market to BE traded for, how old were they when they did, were they already declining when they did, what is the state of the team they went to, on down the line. I don't think between us all we could list every possible thing that could affect whether a team wins a SB in a more significant way than how they acquired their QB, either, excepting that how they acquired their QB might be an indication of the state of that franchise (total guess, who knows!).
To the specific QBs eh. I lean towards thinking Stafford is more likely to blow up in our faces than not and I might be inclined to take my coin-flip in the draft in that case. Watson, to me, is an outlier. If he manages to force Houston to trade him he is a demonstrably outstanding QB who has shown he can play well in poor situations and is what, 25? Our set of QBs to compare him specifically to is much, much smaller and I believe his risk is significantly lower than anyone we're going to be able to draft. If he can be had for a price that the Panthers think is justified by that lower risk I'll do cartwheels. I have no realistic expectation that happens - but one can dream.