So first of all, they sent Aokiji prior to Water 7 for Robin (presumably because they viewed Robin as the more immediate threat given rhe dormancy of Luffy's fruit for the past 800 years). Luffy ended up escaping Aokiji becuase he (and Garp) made a sigificant impression on Aokiji. Sending Aokiji kills two birds with one stone, but Luffy, as he has every at every turn, manages to escape.
Saying they haven't sent a serious force is just a flat out lie, and again, the reason that they send that force does not matter. It does not increase or decrease their overall strength or ability. Your supposition about Akainu is also false. The could have ordered him to kill Luffy without him knowing why, and would have acted the same way.
Do you even read the story? Are you entirely unaware that Dragon had a spy among the Warlords, which is one of the World Government's best weapons and each Warlord has the autonomy to act as they please? If he has people that high up, you think he wouldn't have more? And that if he was aware of their
interest in Luffy that went beyond just his family, that he wouldn't intercede and couldn't make it in time? Get out of here.
Further, i like how you shifted all the way to Luffy dying as to avoid what i was talking about - Dragon, their greatest threat, in possession of what turns out may be one of the biggest threats to them in their long history.
Your argument is just a ridiculous hill to die on.