Scrabble's skill ceiling is shockingly high. Competitive players have memorised every two-letter word, every Q-without-U word, and the optimal tile management strategy across all 100 tiles.
The single biggest skill gap in casual play is the two-letter words. There are about 100 valid two-letter words in the standard dictionary, and most casual players know maybe 15. Memorising the rest instantly doubles your score in tight board states, because every parallel-word placement uses them to stack scoring across multiple words at once.
Tile management is where Scrabble becomes a real strategy game. The seven-letter rack you keep matters as much as the words you play. Hold one S, one blank, and a balanced vowel-consonant mix; dump duplicates and Q/V/Z early unless you can score 25+. The 50-point bingo bonus (using all seven tiles) is where games are won.
The defensive game is what veteran players love and casual players find frustrating. Once you understand bonus squares, you spend half your turns NOT opening up triple-word lanes. A scoring-only mindset gets crushed by a defender who controls the centre column.