I think people are not giving Beguiler enough credit. It shifts a part of your focus generation from attacks to Deception spells. Being able to Mental Binding > Secret Horrors > Eyestrike before having to attack with your weapon a single time is very strong.
I would emphasize that a Mental Binding opening to mess up enemy engagement into Secret Horrors is very strong, especially early in the game.
The main issues with Beguiler are more meta than mechanics.
It is great with AoE deceptions that refund or even generate focus later in the game. In practice that means Secret Horrors and Mind Plague; Honorable mention to Ringleader, though I have been less impressed with the skill now that charm breaks easily.
Outside of those it falls off pretty fast. Mental Binding is a great opener in a lot of fights to mess up enemy formation and engagement, but it loses value past the initial seconds of the fight and drops in priority as you get access to more impactful powers. Eyestrike is fantastic on paper but is badly outperformed by Chill Fog in most groups; Phantom Foes rarely seems worthwhile now that all perception afflictions flank.
The other major problem it runs into is boss fights. While the aforementioned tricks are great early game, most bosses are STR/DEX/RES resistant INT immune, which is a fancy way of saying 'Immune to Beguilers'. Here your lower base focus generation and lower damage (which also lowers focus generation) makes you notably weaker than a core Cipher.
I would argue the biggest benefit of the subclass is how nice it makes Mind Plague, as with the bounces it will consistently return a big chunk of its cast cost, making it a powerful spamable debuff.
It's definitely a reasonable subclass design and does some things really well. I just find it narrow, and the 'much weaker in the hardest fights in the game' is a big enough drawback that I can't ever recommend the subclass to a new player.