@ the OP,
tl;dr I think they work much better in actual play than you might be thinking.
Have you ran one of these yourself or seen one for a reasonable period of time in your own campaign or sessions? I have. I had a player that ran a monk through the entirety of I5 Pharaoh at GenCon. While that is not a lengthy period of time, I can tell you that the monk performed extremely well.
Your initial summary of the monk as a fighter is erroneous. If anything, the monk is an odd mix of cleric and thief. They're not necessarily Eastern in nature, particularly if you've read any Brother Cadfael mysteries.
When compared to a thief though, they start looking much better. Their bonuses to the meaningful thief skills are pretty solid, and the ability to avoid damage at higher levels is very nice. Even at 5th level, they will mitigate a considerable amount of incoming ranged damage (35% of missile fire, considerably more reduction from magical ranged damage). Hit points are kind of meh, but at 7th level, they essentially get a d6+1 pip per level beyond 6th added to their HP total. You're all but immune to pitfalls, which, IME are a major PITA for most OD&D characters. Movement is spectacular. You're very rarely surprised and with reasonable skill, monks are quite skilled at surprising opponents.
Sure Speak with Plants seems irrelevant, but in a game of exploration (which is really what OD&D is about), it can be quite handy. It's not that much of a stretch to use it to track wandering monsters back to their lair (where the loot is). If nothing else, it makes your party virtually impossible to track. Your AC and damage output seems very poor, but as the game goes by, I bet you'll find that they get considerably better. Bracers of Armor will be high on your wish list, as will cloaks and rings of protection. Most mid level parties end up w/ items like that, so it's not unreasonable to think you can acquire them. By the time your damage dice gets up to d8 or so, you can become a very solid hit and run combatant. You've at least a 15 Dex and the best movement in the game, only horses and such will be able to keep out of your short range (for a further +1 to hit). Once the bad guys have been whittled down, you move in and hope to get lucky with your HtH strikes. Stunned opponents die very quickly, and occasionally, you'll flat out slay a dude or two.
I think their biggest drawback is the fact that, along with the Paladin and Ranger, they are very difficult to roll up. Their basic attack bonus is also very low and they don't enjoy bonuses to EPs so advance a bit slowly. Hit points in practice are much better than they might appear due to damage mitigation and the healing ability. Additionally, beyond name level, they're one of only 3 classes that continues to roll hit dice AND enjoy a bonus from CON. I think they're fine as is and are great fun. It's bonkers to compare them to fighters when they are a subclass of cleric w/ a bit of thieving ability to replace the spell casting of a cleric. IME they are far more capable combatants than either clerics or thieves.