Are our prayers so lacking in content and context that without adapting the words to music, even when it requires repetition of the words in order to keep to the tune so very necessary? Is it even basically legal?

In general it is definitely better not to repeat words when speaking to G-d in prayer, just like when speaking to a person we don't do so. Prayers should be heartfelt whether with tunes or without, and everyone should pray in the most meaningful way possible! Most find that varying our davening is helpful to prevent it from becoming rote (which is the biggest challenge, but there are solutions!), sometimes singing, sometimes saying slowly, sometimes saying each word fast so as not to let outside thoughts distract, etc. etc. Many find preparing for prayer is helpful, e.g. listening to meaningful music and concentrating about what we are about to do. In short, as with most important topics in life, everyone must sit down and have a "game-plan" how to do it in the best possible way. As I wrote previously, every rabbi must decide in his shul what are the guidlelines.