1. i would imagine that since its an mmo, as a single summoner the FFVII way of a big attack and leave functionality wouldnt work because unless the summoner has many summons in his possesion a single attack might not kill the enemy and even if it did, it wouldnt be very enjoyable.
2. i believe in FFX you only control the summon and you cease to control your main character which would be ok because it adds a second level of keeping your character in a safe spot while you control the summon, so i would imagine that would work pretty well.
3. the FFXII (though i havent played all of that one) of summoning a primal (or fraction of the primal) and it attacks on its own would become boring if the player character himself does not have actions and abilities that he can do himself while the primal is attacking. that would also be very difficult to use because of the lack of control in a party, and very hard to balance on the dev side
4. and the last one which you mentioned the funcionality on your second option which is like FFXI, where the PC does have abilities and actions that they can perform and control the primal at the same time. or at least the PCs actions are to control the primal but you are still in control of yourself and can attack along side it. would be easiest to implement, has the most control, and wont be too hard to balance.
though farely close is the second option listed, because it allows exact control over the battle since you just focus on your primal control, and adds another element of keeping your PC in a safe spot, though this doesnt meet up to the 4th option as much because in this way it would be difficult to solo, if your in a dangerous area you would be unable to escape quickly and also when you get aggroed you wont be able to fight back.
because of all this i think the fourth option is most suited for the mmo genre but option 2 is also good with a few things that would need to be worked out