An ex-GF of mine complained about that very pub, 25 years ago, for the very same reason.
> only Smith's inferior substitute.
She was wrong, and you are too. Guinness is an indifferent to bland stout and the Sam Smith's Oatmeal Stout is a vastly better example of the style. Widen your palate, learn to appreciate variety and diversity, and recognise that brands are your enemy, in beer just as much as in social networks or political parties. Slavish loyalty to any brand is rank foolishness. Even if you do like it, your life will be better if you learn more about the wider options.