This is a very important note.
The difference between 4th and 5th level characters can be MASSIVE. Many characters DOUBLE their offense at this level (through extra attack). Suddenly spells like fireball are options on the field.
Further, I also find 5th level is generally where PC hitpoints are high enough that the chance of dying outright from a single attack drops markedly, aka generally only a really powerful crit still has a chance.
Its telling that on the chart, the CR of solo monsters increases by full 5 points comparing a 4th level party to a 5th level one.
And it is the point, where any single classed character beomes about twice as powerful:
- spellcasters gain level 3 spells which are way better than lvl 2 spells and cantrips double their damage. The bard gets the lowest power leap, but gets short rest inspiration which does not help too much on a single fight, but still allows you to use them without hestiation.
- barbarian, fighter, monks, rangers, paladins gain extra attack and the latter two also gain level 2 spells. The monk gets stunning strike amd the fighter 4 attacks in a nova round.
The barbarian probably gets the lowest jump, but fast movement does get in handy.
- that leaves the rogue, who "only" gets 1d6 more sneak attack damage offensively. But uncanny doge more or less doubles the hp. Also expertise skills will go up two points which make dex based skills a lot more reliable (they are usually at +10 by then, which often is an auto success).
That leaves the artificer, but besides two classes having extra attack and second level spells, the other two have potent cantrips and some other tricks at their sleeves. So yes, overall they are probably twice as powerful as 4th level characters.