Admittedly, lookout is lesser-used compared to the other slots, but its use is wider than you make it sound. It has a more nuanced function and require good knowledge of your opponent’s options, but so does many other areas of Codex play. It doesn’t mean that it’s a gimmick that only gets explored by highest-level play. I think in certain situations its usefulness is pretty apparent - whenever the Lookout is physically safe but vulnerable to spells/abilities Lookout is better than the backline, and even better than the resource slots if the unit won’t die/you want it to survive.
A hopefully helpful reference list of what Lookout is effective against in the game, not counting effects that kill illusions:
Lookout things
Growth: Polymorph
Neutral starter: Spark, Bloom, Wither
Bashing: Intimidate, The Boot, Final Smash, Hired Stomper, Trojan Duck
Finesse: River midband, Appel Stomp
Red starter: Bombaster, Careless Musketeer, Bloodburn, Scorch (more effects than Black/White starters combined)
Anarchy: Zane maxband, Calypso Vystari
Blood: Bloodlust, Kidnapping, Crash Bomber, Ogre Recruiter
Fire: Jaina mid/maxband, Firebat, Bamstamper Lizzo, Firehouse
Blue starter: Arrest, Porkhand Magistrate
Law: Bigby midband, Insurance Agent, Arresting Constable
Peace: Boot Camp
Truth: Hallucination, Mind Control
White starter: Grappling Hook, Snapback
Discipline: Grave maxband, Versatile Style, Reversal, TPoS
Strength: Thunderclap, Entangling Vines, Whitestar Grappler
Black starter: Deteriorate
Demonology: Vandy maxband, Shadow Blade
Disease: Orpal mid/maxband, Sickness, Crypt Crawler, Ghoul
Necromancy: Nether Drain, Doom Grasp
Purple starter: Forgotten Fighter
Past: Prynn maxband, Vortoss Emblem, Undo, Origin Story, Stewardess of the Undone, Ebbflow Archon
Present: Geiger maxband, Tricycloid, Octavian
Future: Reaver, Xenostalker, Nebula
Some areas may only have one relevant card, such as Growth’s Polymorph or Purple starter’s Forgotten Fighter, but their existence is important enough that one needs to consider the Lookout slot when patrolling for that single card. Putting a Ironbark Treant in Lookout instead of Squadlead when you needed to patrol may make the difference between a setback for you and a bad trade for your opponent when they have Forgotten Fighter around, and that’s something the other slots can’t achieve. These considerations will become more apparant and natural with more plays. It does take more knowledge and thought, but is in no way a slot reserved for the experts.