I agree complete control of a situation isn't entertaining... which is also only ever achieved with cheat codes; ie Power Overwhelming (invulnerability) in StarCraft 1. However, I said when the player feels they are in control of the situation, not when they know they have complete control. For example, take Dark Souls 1. If you run through a specific area enough times, and know enemy moves and where enemies are, you can feel in control of the situation and can often roflstomp your foes. Doesn't mean you are in complete control, as the AI will on occasion do something different and doesn't mean that the player can make mistakes and turn a controlled situation into an uncontrolled one. However, a player will reasonably feel that they are in control. I make the difference between feeling and knowing, because they are very different. You would have complete control of the situation in Dark Souls, if for example you were invulnerable and thus couldn't be killed.
A lot of games fall under that though; they have fixed encounters, with foes with fixed values, and will react in the same way everytime. A lot of AAA games have eschewed with randomness and have fixed values and thus replaying the game will play pretty much exactly the same. Take as an example, Mario. It is completely fixed encounters and mechanics, and yet people find it fun even to this day. True, its not technically a RPG, but games can be fun when they are deterministic, and always fair. Also, there are RPGs with completely fixed mechanics out there that do just fine. As an example, back in the early 2000s, there was a game called Rune, where you played as a Nordic hero in norse times, that had all the trappings of an RPG, but everything was fixed and could always find items in reliable locations. Or take doom (the old one), everything is deterministic there as well. You don't need to have randomness to have fun.
True. That is an issue of First Order Optimal Strategies, which is a hard thing to prevent in gameplay design. There is always one build or style that will be the best, but it may not be the FOOS. As an example, Dark Souls often forces a player to adapt, however, often times the best build is always going to be a spellcaster. Players might try being melee, or stealthy or ranged, but eventually they realize spellcasters are the best and then the game is flooded with spellcasters.
Its not representative of most RPGs, but it is representative of roguelikes. In the case of most roguelikes, from ADOM, to Darkest Dungeon, to Dungeon Crawl Stone Soup, to Rogue Legacy, the game often will introduce pure randomness into the game, making player choices often irrelevant and I can assure you that is not fun. Its painful to have your character wiped out, due to a situation out of your control or lack of knowledge. As an example, in ADOM, if you get to the level with the Banshee in the caverns of chaos, and don't have beeswax in your ears, you insta-die. If you know of the banshee beforehand, such as you've died to her before, but can't find any bee hives to collect beeswax, you are in fact screwed. You could argue that player inputs could have a mitigating effect, but it is often minor compared to the effects of the RNG. Or take Darkest Dungeon, you can have an extremely well prepared and well designed group with proper skills, but the RNG can decide to kill off three of your characters, within the first round of combat, before you have a chance to do anything.
Im doing controlled randomness... so I don't understand why there is a problem. The players actions and choices do matter and proper usage of resources, will help to ensure success but not determine it. Monsters are created with a decent amount of variance to their stats, so just being able to kill a LV 2 primal wasp, doesn't mean you will have a guaranteed success against the next one, but coming properly prepared will improve your odds. I do have carefully controlled events, and thus I am able to assess how quickly a player progresses in the game. Well, I'm trying to get a balance between deterministic and random, so if I'm not achieving that, then that is where I'll make modifications to push it from one extreme back to the middle ground.