That shows how poorly you've comprehended what I said, since I never said anything along the lines of "Becoming Pirate King means you can solo Admirals" or "Helping someone become Pirate King means you can solo Admirals." If you're gonna try again to be a smartass, don't emphasize the second syllable next time.
What did Luffy do without his crew? Are you referring to Marineford and Impel Down? Because, last I checked, Luffy horribly failed at Marineford. Ace ended up dead, he ended up an inch from death several times, and was unable to do anything during the war. The only thing Luffy accomplished at Marineford was freeing Ace from his cuffs(which doesn't matter because he couldn't save Ace anyways) and impressing those around him with Haoshoku. If it wasn't for Ivankov rejuvenating his energy, Luffy would have been KOd by Kizaru and died before the war was even halfway over. In Impel Down, Luffy's best individual effort landed him in a pool of poison and thrown into one of Impel Down's harshest levels. You know what Luffy's individual strength would have gotten him? Magellan would have been his last fight. Ever. The only reason Luffy made it out of Impel Down alive and even survived to regret his failures at Marineford is because of Ivankov, Crocodile, Jinbei, Bon Clay, Buggy, Mr. 3, the Whitebeard Pirates, their thousands of allies, and the other Impel Down inmates. So no, this does not help Luffy's individual strength argument whatsoever, you actually crippled it two times over by using an argument that has nothing to do with Roger in the first place, and it being an argument that doesn't even hold up.
Roger didn't become Pirate King on his own. You're basically saying "Roger was charismatic enough to convince people to help him become Pirate King, so he became Pirate King by himself."