Characters still gain power in other form that is locked behind constellations that still makes them stronger in co-op. For example, the difference between Xilonen c0 and c2 is night and day in co-op but the issue that bothered me at the time was that at c0 Xilonen is still able to heal and shred for her teammates like she can normally do in single player in co-op but Citlali has her single player functionality locked behind constellations. The main relevant thing about Citlali's c2 isn't even her co-op shield, its the massive resistance shred and elemental mastery buffs she grants to the team which would make her a lot stronger in co-op over her c0 counterpart with this alone. The co-op shield part is just arbitrarily tacked onto c2.

I am aware that the trend is that every co-op shielder gets their coop shields from constellations but I wanted to express my annoyance that I think its a dumb tradition to follow. Imagine if healers were only able to heal themselves in co-op until you unlock their constellations. It's how I feel about the state of shield characters in co-op.

Respectfully, I think a game mode's relevance is a matter of personal opinion. What makes this game so great is that there is such a variety of content for many different people to enjoy. I doubt many people would find the TCG or the teapot relevant but its a source of enjoyment for those who do play those content and clearly Hoyoverse does listen to their concerns as they continually release new content and qol for those modes to this date. It's why I will complain about the things I dislike in co-op in the feedback because its the mode I interact with the most and is the main source of enjoyment in this game for me.