the lions won 3 times in the 50s in a 12 team league. other than that, thry have won one game in the postseason in 1991 and then were blown out the next week. they also play in a league with a salary cap and draft designed to make all of the teams equal, and they have the least amount of success of any franchise in that league's history.
the cubs won the national league title and went to the league's championship series seven times before 1946. they won two playoff "rounds" in 2015 which is more than the lions, and have won numerous "playoff games" in between their trips to the world series, although with many more chances.
it is also much harder to make the playoffs in baseball historically than football. the nature of football and the league changing the rules for more playoff teams, a harder salary cap, and a draft to distribute the best talent to the weakest teams (and the speed at which that talent can make a difference in football as opposed to baseball) makes it easier to achieve success in the nfl than in mlb.
look, they both suck and this is a silly argument, but given the inherent structural advantages the nfl grants to teams as opposed to mlb historically, i would say the lions futility is at least equal to the cubs, and imo, greater.