Well I agree with your first point, They would atleast need to eatablish supremacy in Deccan to be considered powerfulWell yes, I have said that almost essential for mysorean geopolitical supremacy is the Carnatic and kicking the British out of Madras, which otl they very much proved they had the ability to. The Vijayanagara example also works even if Mysore doesn't have Kerala because the region was effectively independent from Vijayanagara, only bound by loose tributary relations.
Amphibious operations are essentially impossible, so European naval supremacy doesn't touch the land based state, and European trained armies on the mainland can be dealt with by Mysores modernising military, as shown otl.
Amphibious assaults are hard, but not impossible, and this is at the start of European imperialism in India, Europe would have all the advantges to India in terms of navy, unless Mysore produces a defensive navy, They would be screwed European navies