There was a huge and underappreciated shift in design philosophy from Generations 1 and 2 to Generation 3 that is ultimately responsible for a lot of the series' problems right now, imo. I want to dive into monster design (primarily) to explain why that is. Jump down to E. Summary if this is too long.

A. Generation 1

Generation 1 is remarkable for a large number of well-rounded monsters that often stand out only in Speed as a basic stat, especially early in the game. Critical Hits bypass stat modifier moves and effects, and deal anywhere from +50% to +95% damage, based on your level; your chance of a critical is based on your species' Speed value. The way this math works out, all species grow increasingly deadly towards the end of the single-player game, and notably high speed is worth about 8% more damage on average for most fully evolved monsters, with more variance for exceptionally slow final forms. Overall, it's not the biggest difference in the world, but it is a difference that exists.

Also of note was the fact that tight move availability was built into the system and accommodated for; all TMs were supposed to be attainable only the once, which meant the expectation was that most monsters would use Normal moves as their bread-and-butter if their type moves weren't effective on the situation.

It was therefore reasonable to carry multiple of the same type of move on monsters during the story mode; you used Flamethrower, Surf, Ice Beam, Fly, and Strength for ordinary scenarios due to their high PP, accuracy, and availability. Fire Blast, Hydro Pump, Blizzard, Sky Attack, and Hyper Beam were the original 'Z-moves', notable in their especially dramatic visuals for the Game Boy; the ultimate attack of the Fire-type being in the literal shape of a Chinese character for a sacred Japanese festival is about as shonen as it gets, and 5 PP is just not enough to go through a dungeon with that as your key attack.