Unity does not mean that the things joined are necessarily distinguished by quantity. It's as simple as that.The TSKS construction is valid in that it does indicate a unity. You may be interested in my take on the context when presented with this argument.
It's not just epiphinea. It's the blessed hope and appearing of glory. Note the TSKS? It's The Hope and Appearing that is one thing, not just appearing. And it's hope and appearing of glory.
The closest parallel with those two words is in the same book, Titis 3:4-7.
The kindness of God appeared (verb epiphaino) is in verse 4 and results in saving through Jesus (v6) which results in the hope of eternal life (v7).
This is the hope and appearing of God and Christ from Titus 2:13.
This is a parallel from the next chapter of the same book that explains hope and appearing at Titus 2:13.