I agree that Arminius always felt himself to be within the Reformed confessions.
That was what he was arguing for, to bring the Reformed back to the Bible, and not be defined by Calvin's Institutes (BK3).
The term 'Reformed' is used to distiquish the Calvinistic from the Lutheran and Anabaptist traditions. The Reformed traditions finds it roots in the theology of Ulrich Zwingli, the first reformer in Zurich, and John Calvin of Geneva,....( Concise Evangelical Dictionary of Theology, p.423)
Vance writes (quoting Bangs in his work on Arminius) that Arminius deserves to be classified as an orthodox Dutch Reformed theologian.(p.131, Other Side of Calvinism)
Arminius' had great respect for the Institutes.
His studies mush have revealed a broader scope to Calvin's theology than the dortists are seeing.
As many quotes as I've seen from Calvin on these pages over the years ...quotes that appear contradictory to dortist positions...I'd be inclined to investigate my sense that Calvin's broader theology was not misunderstood by Arminius.
And you are certainly correct. Arminius is right that "reformed" is far broader than dortists might try to suggest.