No worries. As a general assumption for damage builds, you'll generally have a 16 in your attack stat for Tier 1, an 18 somewhere in Tier 2, and a 20 by tier 3. Fighters a little earlier, builds with heavy feat investment might be delayed.
Using feats in generally a prerequisite for really high sustained damage builds, as you'll almost always need either the Sharpshooter or the Great Weapon master feat to pull it off. The only real exception is Warlocks and Sorlocks using Eldritch Blast.
The highest (semi-)sustained damage build for tier 3 I can think of is a Hexblade Divine Soul Sorlock using Darkness/Devil's Sight to gain advantage on a cursed target. Using twinned Eldritch Blast, that would be 6 attacks at 1d10+9 baseline, with triple advantage (assuming Elven Accuracy and a half-elf). That's about a 90% chance to hit assuming a moderately armored target, and a 27% chance to crit per attack. You could also use Spiritual Weapon to get an additional 1d8+9 attack, or 2d8+9 if you're willing to upcast. It's only semi-sustained, of course, but it's a damn good trick against one enemy that needs to go down.
The only other really high damage build I can think off is a Zealot Barbarian leveraging Reckless Attack, Great Weapon Master, and probably Polearm Master. GWM and Sharpshooters are also really good, but don't have on-demand advantage.