You left out the key line of Swayne’s opinion: “Upon the merits of the case, I agree with the majority of my brethren.” Even if Swayne and Miller didn’t agree with Chase’s reasoning, they agreed with the decision. That makes it 7-1.
Sigh. They agreed that Texas could not maintain an original suit, ie. that Texas did not have standing to file suit in the US Supreme Court. Why? Because she wasn't a state in the union. If she wasn't a state in the union, it was either due to one of two choices, viz, secession (voluntary withdrawal), or the state was ejected from the union, a violation of Article V ['no State, without its Consent, shall be deprived of its equal Suffrage in the Senate'].
Despite the absence of the required signature, the US treasury redeemed 4 of the bonds held by Birch, Murray & Company, and 34 held by John A. Hardenberg. So on one hand we have the US Treasury recognizing the validity of the Texas' legislatures Act, and the court denying their political recognition. The Court did not hold that those same bonds be returned to the state of Texas. Justice Grier sums up quite nicely the fact that Texas was not a member of the union.
Justice Swayne had wrote, 'The question, in my judgment, is one in relation to which this court is bound by the action of the legislative department of the government.' Congress had instituted military governments excluding Texas from congressional representation. 3 justices agree that Texas was not a state, not a member of the union.
On the merits, ie. the ownership of the bonds, the justices agreed.