At first, the Strawhats make an alliance with Heart Pirate, and then after Dressrosa Arc we are introduced to the Strawhat Grand Fleet. What I want to ask is: does the Strawhat Grand Fleet have equal status as the Heart Pirate, or lower?
Though there are no sources, we can surmise the difference in the nature of relationships between Luffy and Law and Luffy and Straw Hat Grand Alliance.
Straw Hat-Heart Alliance was formed on Punk Hazard by their two captains in order to defeat Kaido, one of the four Yonko of the New World. According to Law, who proposed the alliance, their cooperation would give them a 30% chance to defeat the Yonko.
The Straw Hat Grand Fleet is a fleet formed by seven organizations who vowed to serve under Monkey D. Luffy and the Straw Hats. These seven organizations are represented by
1 Cavendish - Beautiful Pirate (75)
2 Bartolomeo - Barto Club (56)
3 Sai - Happo Navy (1000)
4 Ideo - XXX Gym Martial Arts Alliance (4)
5 Leo - Tonta Corps (200)
6 Hajrudin - New Giant Warrior Pirates (5)
7 Orlumbus - Yonta Maria Grand Fleet (4300)
The key difference to note is the missing objective in the second. Luffy-Law alliance was formed for the purpose of defeating Kaido, one of the Yonko, so they could go closer to the title of Yonko themselves and hence the Pirate King. They are still rivals (Friends/Enemies) but while they are pursuing the same mini objective (defeat the Yonko) they are co-operating with each other. The members of Grand Fleet would support Luffy unconditionally.
Pirate Alliances in One Piece is an interesting read. Some important points
- The captains who formed the alliance are theoretically equal in status, and cannot give each other orders. They may have limited control over each other's crews, but the highest authority still lies with the respective captains.
- An alliance is usually formed with the purpose of reaching a specific, mutual goal. It may be something that neither crew could accomplish on their own
- A common problem with pirate alliances is betrayal; when one captain sees no more use of the other, it results in treason in order to reduce the needs to share glory.
Thus we can surmise Luffy and Law share the status of EQUALS, while those of the grand fleet share the status of SUBORDINATES. Also note that this objective has been extended on request of Momonosuke, since Kaido is holding the Shogun as well, dubbed as Ninja-Pirate-Mink-Samurai Alliance
Extended Question in Comments So, the Grand Fleet are subordinate Law too?
The short answer is No. The Grand fleet is oathsworn to Luffy, but they are in no obligation to follow even when they are in alliance.
However, this often comes out to nothing since Law has the brains and judgement and the leaders of fleet have enough sense to follow those orders. The wikia however also states
In a situation where one of the captains gets captured, the other can take charge of their remaining subordinates.
Thus in adverse scenarios, Luffy's Crew and subordinates may listen to Law because of his status as a captain of an allied crew, but they can have their own judgements.
I made a poor example of Shanks and Whitebeard, but it does help to illustrate my point. They both are Yonko, Whitebeard's Generals know that Shanks is allied to their interests (The battle with Kaido). But they do not follow Shanks after the death of Whitebeard but Marco instead. Also note they DO retreat after Whitebeard's death because what Shanks said made sense. Though he did threaten the consequences.