diff --git a/lib/class-wp-theme-json-gutenberg.php b/lib/class-wp-theme-json-gutenberg.php
index 4d2a0c5129aaa1..76abf3fb473a76 100644
--- a/lib/class-wp-theme-json-gutenberg.php
+++ b/lib/class-wp-theme-json-gutenberg.php
@@ -2771,16 +2771,6 @@ public function merge( $incoming ) {
 				$prevent_override = $preset_metadata['prevent_override'];
 				if ( is_array( $prevent_override ) ) {
 					$prevent_override = _wp_array_get( $this->theme_json['settings'], $preset_metadata['prevent_override'] );
-
-					/*
-					 * For backwards compatibility with presets converting from a hardcoded `false`
-					 * for `prevent_override` to a path to a boolean (`defaultFontSizes`, for example),
-					 * the 'merge' value for the new setting both overrides the preset and tells the
-					 * UI to continue to display a merged set of the default values.
-					 */
-					if ( 'merge' === $prevent_override ) {
-						$prevent_override = false;
-					}
 				}
 
 				foreach ( static::VALID_ORIGINS as $origin ) {
diff --git a/lib/class-wp-theme-json-schema-gutenberg.php b/lib/class-wp-theme-json-schema-gutenberg.php
index 728dd32227798d..fcc43764264f43 100644
--- a/lib/class-wp-theme-json-schema-gutenberg.php
+++ b/lib/class-wp-theme-json-schema-gutenberg.php
@@ -116,7 +116,7 @@ private static function migrate_v2_to_v3( $old ) {
 		if ( ! isset( $old['settings']['typography'] ) ) {
 			$new['settings']['typography'] = array();
 		}
-		$new['settings']['typography']['defaultFontSizes'] = 'merge';
+		$new['settings']['typography']['defaultFontSizes'] = false;
 
 		// Set the new version.
 		$new['version'] = 3;
diff --git a/packages/block-editor/src/components/global-styles/typography-panel.js b/packages/block-editor/src/components/global-styles/typography-panel.js
index 8ccb48c98fa90f..f0dac28335df57 100644
--- a/packages/block-editor/src/components/global-styles/typography-panel.js
+++ b/packages/block-editor/src/components/global-styles/typography-panel.js
@@ -22,7 +22,7 @@ import TextTransformControl from '../text-transform-control';
 import TextDecorationControl from '../text-decoration-control';
 import WritingModeControl from '../writing-mode-control';
 import { getValueFromVariable, TOOLSPANEL_DROPDOWNMENU_PROPS } from './utils';
-import { setImmutably, uniqByProperty } from '../../utils/object';
+import { setImmutably } from '../../utils/object';
 
 const MIN_TEXT_COLUMNS = 1;
 const MAX_TEXT_COLUMNS = 6;
@@ -111,21 +111,6 @@ function useHasTextColumnsControl( settings ) {
  * @return {Array} The merged font sizes.
  */
 function getMergedFontSizes( settings ) {
-	/*
-	 * Backward compatibility for theme.json v2 is triggered by the 'merge'
-	 * value added during the migration process. The old behavior that didn't
-	 * match the other preset controls was to list the partially overridden
-	 * default font sizes. The new behavior either shows all the default font
-	 * sizes or none of them.
-	 */
-	if ( settings?.typography?.defaultFontSizes === 'merge' ) {
-		const fontSizes = settings?.typography?.fontSizes;
-		const mergedFontSizes = fontSizes
-			? mergeOrigins( fontSizes ).toReversed() // New array because mergeOrigins result is cached.
-			: [];
-		return uniqByProperty( mergedFontSizes, 'slug' ).reverse(); // In-place reverse to save memory.
-	}
-
 	const fontSizes = settings?.typography?.fontSizes;
 	const defaultFontSizesEnabled = !! settings?.typography?.defaultFontSizes;
 	return [
diff --git a/phpunit/class-wp-theme-json-schema-test.php b/phpunit/class-wp-theme-json-schema-test.php
index 19deb1acdfdddc..8274b1abe2f802 100644
--- a/phpunit/class-wp-theme-json-schema-test.php
+++ b/phpunit/class-wp-theme-json-schema-test.php
@@ -120,7 +120,7 @@ public function test_migrate_v1_to_latest() {
 					'width'  => false,
 				),
 				'typography' => array(
-					'defaultFontSizes' => 'merge',
+					'defaultFontSizes' => false,
 					'fontStyle'        => false,
 					'fontWeight'       => false,
 					'letterSpacing'    => false,
@@ -293,7 +293,7 @@ public function test_migrate_v2_to_latest() {
 					'width'  => false,
 				),
 				'typography' => array(
-					'defaultFontSizes' => 'merge',
+					'defaultFontSizes' => false,
 					'fontStyle'        => false,
 					'fontWeight'       => false,
 					'letterSpacing'    => false,