Is the statement: "So-and-so is good in this field, but has not yet reached the levels of that field" considered backbiting?

One should not speak ill of someone they dislike unless there is an overriding benefit, such as giving advice. Otherwise, it constitutes prohibited backbiting. The Salaf (pious predecessors) were very cautious in this regard, and they would seek God's forgiveness if they backbit about someone unintentionally. Nothing compares to safety, and the general rule is that unless speaking is clearly superior to silence, silence is preferable, as the Prophet, peace and blessings be upon him, said: "Whoever believes in God and the Last Day, let him speak good or remain silent."