Those titles, just like Bounties... are there for hype for fans... don't be so angry LOL, chill...
Oda also realized he was fucking up when he was gonna make bounties over 300 mil have small increases.... people were disappointed that Luffy from punching celestial dragon, into breaking impel down prison, freeing many prisoners, escape, then marineford war, his infamy became so huge, revealed as Dragon son... then all of that was to increase him to 400 mil..... then Dressrosa arc happened, and Luffy only jumped to 500 mil.... people were SO DISAPPOINTED specially with the length of the arc, and the pay off of bounty was so low...
resulting in Oda changing his mind about bounties increase being low, and he introduced Jack having a bounty of a billion, then Katakuri and Luffy's next raise was to 1.5 billion... only to reveal Yonko later on having many billions...
These tremendous increases resulted in getting back the enthusiasm regarding bounties... and thus, it maintained it's importance by fans...
Titles are same, they are not the all be all... but it gives MAJORITY of fans their hype for what's coming to be enthusiastic and to be welcoming for what's about to come and not feel that the level of what's to come is already met from previous opponents... thus Oda will surely introduce such title in future like "Strongest entity" or generalizing more to be "in history" where he includes all eras...
these type of stuff Oda will 100% play on in future for the hype to continue for fans... it's Shonen 101 subject LOL