Show me a widely used font which contains both U+03C6 and U+03D5.
That was not the issue. The issue is when font wanted to add 03D5 that they would not just put the opposite glyph into 03D5. Or just end up having a duplicate glyph. Fonts that have 03D5 by their nature should be intended for use with technical publishing and therefore are not (as) free in their choice of glyph for 03C6 as pure text fonts are.
A./
