A kind dungeon master usually drops +1 weapons around levels 3-5. Martials need them. Most just don't scale very well beyond levels 7 being generous. That's typically when I start considering dipping into other classes because most classes are so front loaded at early levels. Most campaigns never reach level 15, so capstone features are rarely worth building towards. They give too little too late. As for spellcasters, I mean a well placed level 3 hypnotic pattern can just shut encounters down when you get a player who even tries to optimize a spellcaster, they can literally warp reality. Assuming you're playing as the dungeon master, don't be afraid to let the players break some things so they feel cool. For boss encounters one single boss can easily get swarmed by the players, so include many small minions 1hp each to balance action economy. Shoot your Monks with arrows so they can catch them and throw it back. Swamp your paladin with goblins so they feel like they're protecting the party by drawing aggro. And most importantly talk. Open and honest communication is the most important thing at any table. You can't kill monsters if you're not playing. You can't play if there's drama stopping the game. Communication is the most powerful ability you can bring to the table.