OB1
Jedi Master
Does it really need to be?
If it is required, yes.
It's not hard to confirm that, just look at the monsters: Do their attacks scale from a +4 at CR 1 to a +8 at CR 20? Do the saves they force scale from DC 12 to DC 16?
Why compare monster attack bonus and save DC to PCs? Monsters have Abilities over 20, which PCs don't. Let's instead compare the defenses that the PCs need to hit between Level 1 and Level 20
CR 1 Brass Dragon - AC 16, Saves - Dex +2, Con +3, Wis +2, Cha +3
CR 20 Brass Dragon - AC 20, Saves - Dex +6, Con +13, Wis +8, Cha +10
The AC has scaled perfectly in line with Prof increase, meaning it's just as easy for a Level 1 PC to hit a Brass Dragon wyrmling as it is for a Level 20 PC to hit an Ancient Brass Dragon without any increase in their Primary Attack Stat.
Saves are all over the place due to ASIs in the Dragon's stats, which have increased a total of 40 points, or 20 total ASI bumps, almost 3x more than even the fighter gets, meaning a 1:1 comparison between monsters and PCs cannot be made. However, just for fun, let's look at the probability of the Ancient Brass Dragon making it's saves against a Wizard with a 14 INT vs 16 INT at 1st level and 14 INT vs 20 INT at 20th level.
1st Level
14 INT DC 12 - Dex 55%, Con 60%, Wis 55%, Cha 60%
16 INT DC 13 - Dex 50%, Con 55%, Wis 50%, Con 55%
20th Level
14 INT DC 16 - Dex - 55%, Con 90%, Wis 65%, Cha 75%
20 INT DC 19 - Dex 40%, Con 75%, Wis 50%, Cha 60%
Any save involving these is a crap shoot for the PCs regardless of level or intelligence and a mere 1 out of 6 castings will end in a different result for the two wizards at 20th level. Is that worth 2 Feats? Or not having to pick between maxing Con (for Concentration and HP) and Dex (for AC and Initiative)? Or wearing Medium armor for the entire campaign? I'd say the choice is a lot closer than people think.
I agree that there is nothing wrong with meandering to 20.
Or even taking a path that never gets there!