It's not an unreasonable question. He is most certainly in the conversation.
He's ahead of most of the all-time great goal scorers in goals/game. Ignoring numbers 3 and 4 on the list below, who played almost a century ago, Matthews is only behind Bossy and Lemieux.
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He is well ahead of his contemporaries who are considered great goal scorers - McDavid, Pastrnak, Draisaital, Connor, Rantanen.
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So if you accept that Matthews is the greatest goal scorer of his generation, because it's fairly obvious he is, then it's a matter of comparing eras to answer the question of who is the greatest in history.
As I stated above, Matthews is definitely in the conversation, if he continues producing.