The tradition of summoning an extraplanar entity to bargain with is well established in the D&D lore. But they don't necessarily like being summoned for this purpose, which is why wizards usually bind them in a magic circle so they can chat without having anyone's head bitten off.
In 3.5e, at least, this was fairly simple. Gate got you the outsider of your choice, friendly to you. The Planar Binding series of spells got you your demon/devil/slaad/whatever, and a Magic Circle against Evil with a calling diagram kept it contained. Then you could make a bargain with it, it could try to twist things in its favour and screw you over, and a good time was had by all.
However, times have changed. Gate in 5e summons an outsider without restricting its actions in any way. Planar Binding will bind a summoned outsider, but specifically requires that it be in range for the 1 hour it takes to cast. It explicitly calls out a Magic Circle as the way to keep your summoned creature captive while you do this, but a Magic Circle doesn't protect you the way it used to. It will prevent the creature from affecting your mind, hold it in the circle, and give it disadvantage on attacks. On the other hand, the creature is free to cast spells, and if you're casting for an hour (600 rounds!) there's just no way it's not going to break your concentration at some point.
The Monster Manual notes that devils like to make bargains, but the only currency they will accept is the immortal soul, and that summoning demons is extremely dangerous, but some people still do it. The key issue is that while some outsiders, like devils, are happy to bargain, if they can break out of the circle and get you at their mercy it makes the bargaining very one-sided. 'I will spare your life in exchange for your immortal soul, foolish mortal' isn't the deal I'm looking to make here.
So, have I missed something, or is this incredibly risky method the only way to make a bargain with a powerful outsider?