I guess it gets quite messy who meets with whom, because the Head of Government and Head of State of one country doesn't neatly map to the respective roles of another. For all intents and purposes, the world recognises the German Chancellor as the de facto "leader" of their country. For example, the four Presidents who have visited Ukraine today from Estonia, Latvia, Lithuania and Poland are all from parliamentary republics or semi-presidential systems. Only the Lithuanian President could be described as the de facto leader of their country. They have all only met with the Ukrainian Prime Minister, Denys Shmyhal, as a far as I am aware before touring some towns, although are supposed to be visiting Zelenskyy at some point.
I don't really understand why Germany isn't sending the Chancellor. If you want time with the Ukrainian President, you send your equivalent in seniority, not the secondary guy.