I don't get this part. they're both fantasy. isekai just means someone went to a different world, but it's all under the umbrella of fantasy. So you're saying the characters never went to the other world and it was just a fantasy story? in that case the author should have never tagged it isekai.
There are no intelligent deconstructions of the isekai genre. All isekai have fallen into the same uninspired tropes whether the authors realizes it or not. Breaking the 4th wall and acknowledging that yes the MC has been killed by a truck haha isn't deconstruction the genre nor is making the MC a cool guy or straight up suicidal. Seeing as the only way people can 'subvert' or 'deconstruct' this genre by adding small drama or a threat that gets solved within 2 chapters shows how lousy this genre as become. Stories I read that I thought were isekai were actually just regular fantasy, and good fantasy at that.
Believe it or not, there are wonderful premises and writing for Japanese Isekai with the implications explored.
-Overlord for being the poster of a video game world with a powerful, non-edgy, anti-hero.
-Youjo Senki for throwing a grey/evil person into another world so that they may experience war and change their beliefs, genderbent while at it.
-Hataraku Maou-sama for doing a reverse isekai, with fantasy characters adapting to modern world and incorporating multiple worlds in the story.
-Grimgar of Fantasy and Ash for having the Isekai as a phenemon happening in the setting. The story is relaxing and then shifts into action, tension, adventuring, and serious parts where the cast and world is realistic and immersive.
Others are Re:Zero, No Game No Life, Mushoku Tensei (for being the first of it's kind), Slime (for being a happy-go-lucky action story with mature-ish protag), Mobuseka, Common Sense of a Duke's Daughter (the manga), Märchen der Werwolf: The Annals of Veight, Clearing an Isekai with the Zero-Believers Goddess
CN: Reverend Insanity, Lord of the Mysteries, Kingdom's Bloodline, The Legendary Mechanic, To Be a Virtuous Wife, The Experimental Log of the Crazy Lich, Cultural Invasion into Another World, A Mistaken Marriage Match: A Generation of Military Counselor, QT Cannon Fodder's Record of Counterattacks and all QT etc.
KR: (Mostly male or harem because of demographic for actions stories) Ending Maker, Omniscient Reader's Viewpoint, Legendary Moonlight Sculptor (it is up to you whether or not VR game world is another world, but it mostly works like a real world in this setting) Regressor Instruction Manual, Trash of the Count’s Family, The Second Coming of Gluttony, Dungeon Defense, Holy Emperor’s Grandson is a Necromancer, Isaac, Never Die Extra, SSS-Class Suicide Hunter, etc.
I agree that many Isekai for lazy writing when it could have been standard fantasy, but I do sure love it when the circumstances of being sent into another world are explored and the story succeeds in making it a complex, refreshing, and hooking story with a mature world.
Also, Zombie Land Saga is not an isekai but despite including Truck-kun in the story, it actually is an ingenious part of it which just drew me in from the onset and made me watch it.