Arvis is the only unit here who can run multiples roles with (high) success, even if Catria and S!Ylgr are very versatile, none of them can be as versatile as Arvis.
With what you told us, you need other thing than pure damage/tank, and more prompt of being useful in any situation, and Arvis is exactly what you need. He is one of the best support in feh (for me).
Arvis is a unit who is meh with low merges and start shining at high merges. But even at low merges he can be : Quad ploy boi, combat healer (with his prf B slot and ardent sacrifice) moderate mage tank and moderate offensive powerhouse.
But at high merges with somes DF, he can become (with the same set) : combat healer, WTA breaker mage tank, offensive powerhouse And quad/tri ployboi. He is also very cheap to build (skill-wise)
Nones of your others choices can be as versatile as that, and with his ploy and combat healer, he can be a very powerful addition to your arena core.
On a side note, he work wonderful with saizo
What a high merges high df Arvis look like