I have seen immense difference in effectiveness between a character with multiple attacks, and a range of bonus actions and reactions.
For instance we can compare an elf evoker 6th level wizard with the spell sniper feat who chooses between a cantrip damage or a spell slot each round.
vs
A variant-race Bladesinger wizard who can cast a cantrip damage, make a melee attack, and if they use metamagic adept at 6th level to get an extra fireball in that round as a bonus. Or they can use flaming sphere to attack every round as a bonus in comparison with booming blade to deal additional damage whether they move or not. Plus the Bladesinger is getting AC around 19 with the option to boost it to 24 as a reaction. If they don’t do that they can swipe that foe that moves away from the flaming sphere for another attack/cantrip/spell for more damage using warcaster.
Very little skill is required. With forum and video guides, rankings etc building a frighteningly effective PC just requires opposable thumbs and a computer with internet access.