Roger's biggest opponents: Xebec and Whitebeard, Garp is not even top 2.
What manga you are reading? And even Garp is an anomaly who refused to be a Ladmiral. Somehow Lakainu is suppose to be a bigger rival than Kaido, that Luffy should face him after fighting a far stronger Kaido? Even Law and Kid are better rivals, as Oda put them on front cover, not back cover like Lakainu.
And no, back cover doesn't count where Smoker is also there.
The basic story telling told us Luffy's main opponents are Yonko. Since Sabo is not going to do Luffy's job (fighting Yonko) only left for Flame Emperor Sabo is Lakainu, Lakainu is perfect EoS opponent for Sabo, not for Luffy. Oda even established their opponents according to their DF weaknesses: Luffy's GoD DF can be neutralized by Blackbeard's darkness, Flame Emperor Sabo's Fire DF can be neutralized by Lakainu's magma.
Yes Sabo is a revolutionary and his goal is dethroning Celestial Dragons, who is the top no.1 lapdog of Celestial Dragons?
Lakainu.
https://worstgen.alwaysdata.net/forum/threads/akainu-doesnt-hate-pirates-he-hates-the-enemies-of-the-government-akainus-character-got-exposed.18324/
Akainu doesn't hate Pirates, he hates the Enemies of the Government (Akainu's character got exposed)