"Build X" and "Play X champion class" missions are anti-competitive and poor design
I can either choose to play ranked and ignore the missions, or focus on the missions at the cost of actually using strategy.
"Build a 3* Noble"
Sure, let me get on that. Too bad everyone going for the mission is going to be pulling from the same champion pool. Either I get eliminated early from ignoring the available champions and items to focus on a specific build, or l use all of my econ trying to reroll for a champion I need, both of which are the worst strategies in TFT. I just made it to the final 3, all at ~10hp, because I had a team of 6 Nobles. So did the other 2 players. I spent all game buying every Noble I could find (the game kept giving me shapeshifters so I had a gold Elise really early), and finished the game by selling everything on my bench to try to get the last Garen I needed. Got knocked out. Guess I'll have to try again for another hour.
The "Play X Champions of this Class" missions are bad for the same reason. You're ignoring strategy in order to put in an arbitrary requirement.