In the sense that we are 'tri-' we agree with you. The biggest difference is 1) That the Lord Jesus Christ is called God (there were no capital or lower case letters in Greek) 2) There is only one God/god. (JW's disagree and have many 'gods' as do Mormons and other polytheistic groups).
Compare: Isaiah 42:8 John 17:5 How could such be unless that Glory and One-God somehow existed in some mystery that we cannot quite figure out? Is it a sin to 'try' to figure out what is clearly mysterious and difficult? A triune position is simply this: It doesn't 'try.'
Some Algebra equations can only be simplified, not solved. Anyone attempting to solve gives false information for missing values. It 'may' work on paper, but it is well beyond the ability of the problem given, to solve. Very similarly, we Triune say that the scriptures cannot be solved and either the Modalist or Arian, try to solve by introducing artificial values for God. There is no scripture that says there is a god and a God (can't, remember there are no upper-case letters in original Greek). I tried a few times in Algebra, to 'solve' for X and Y. Though my numbers actually worked in the equation perfectly, I got the answer wrong because I introduced artificial values. Though the artificial values 'worked' it was wrong simply because I closed the equation from any 'other' correct value to be introduced.
Unless and until God gives those actual values, that is, unless we know how John 20:28 works, we are remiss for filling in those values.
2X+1X = T-X You can reduce this to 2X=T but it cannot solve. If 2X were akin to those called "God" and T was given as Only One, you'd have to accept the fact that we can only see "Tri-" and "-une." IOW, it could/would be the only acceptable position. This is why almost all of us are Triune. Logic/reason demands we NOT solve for X or T, simply leave the incomplete picture, incomplete. Further: It is actually wrong/incorrect to try to give false values for T and X. It is wrong to try to explain that the Lord Jesus Christ is 'a god.' It is wrong to try and say God is not Jesus. Why? Because it is impossible, literally, to assert. The answer is clearly wrong. This is why I am not and cannot be arian or modal.