That's a good point, I think it does relate to melee classes and the fact that they are relatively simple compared to spellcasters.
Yes, but that is just unnecessarily bad design, a lot of which is compounded by the fact that there is bad environment design in RPG combat. You're not about to find a warrior with the ability to set up and shift barricades, lay traps, and then push enemies into them. You can do really interesting stuff with that, but most games aren't about to go there and really play around with environmental barriers, hazards, traps that can be forcibly activated by both sides, etc. Combat encounter design is too often treated like an afterthought, unless they're trying to have an "epic" fight and even then they tend not to do too much.
As an example in Baldur's Gate games, you can be extremely overpowered as a mage but there are still enemies immune to Time Stop cheese etc. Moreover, you have low hp and some enemies can still oneshot you. So as a mage you still have to be strategic and plan your spells, spell order etc.
Yes but Baldur's Gate was still a 2E AD&D adaptation. In later D&D editions and Pathfinder in particular, mages exploded in hitpoints and got a lot more spells per day. Most computer game adaptations actually nerf spellcasters pretty hard (huge spell list reductions, immune enemies, saving throw inflation, reduced spell functionality, harder hitting enemies, and way more fights per day than tabletop does, which makes running out of spells a bigger concern) and they still tend to top.
In most games melee classes have few abilities, making them simple. If they became super strong they would become faceroll.
That's what mages often do. If you're selling the power fantasy angle though, there's no good reason why your non-mages fall behind so much. At that stage your warriors should be able to perform awe-inspiring leaps into the air, let out a devastating warcry, throw allies and perhaps enemies into different positions, give your allies some kind of aura just for being in the presence of your greatness, shrug off blows that would fell lesser men, perform a devastating charge that knock lesser foes out of the way, etc.
One step in the right direction would be to add some interesting skills to melee classes perhaps? Or give them special items they can use while in combat. This way it would increase the complexity at least.
Yes, on both counts. Adding intimidation abilities, leadership abilities, reposition abilities, debuff abilities, enemy disruption, DoTs that play to hit and run tactics, maybe some first aid, guard-enhancing abilities, etc. can do a lot to make non-mages feel less like shit. Poisons, bombs (and not just the damaging variety, but also effect-inducing ones), traps, nets, thrown weapons with special effects, caltrops, etc. can spice it up a fair bit. Although you also have to make combat difficult and challenging. There's no point in giving a melee class dozens of interesting ways to mess with enemies through careful strategy as well as an arsenal of debuffing moves and ways to interact with opponents' guard and disrupt their actions if the enemies are a joke and the combat ends faster by throwing him at the enemy and hitting them with your high damage moves until they're dead. If you make intelligent mechanics, you have to give people strong reason to use them. That's part of the trouble with aggro mechanics: they disincentivize clever play by making your enemies stupid. But hey, they make it much easier to get away with bad enemy AI. Never underestimate the power of incompetence in having knock-on effects in game design, and never doubt the appeal of laziness to many designers who pretend to be better than they really are. Clever combat demands cleverness in a lot of fields, from combat mechanics to enemy design to enemy AI to encounter design (which will impact level design) to resource management to gear and consumable item management where any one aspect can impact the rest adversely if you're not careful. There's a lot less work involved in half-assing it.
But if you're just playing a stupid power fantasy where the player character is supposed to be overpowered there are still a number of more interesting abilities you can give non-mages than just variations on hitting something. Just copying stunts from mythology, chinese wuxia, etc. can go a long ways if you're just looking for ways to make your character feel more awesome. I think part of the problem also plays into western fantasy RPGs trying to make non-mages super-mundane while wizards have all the mystical powers. If you want your warrior or whatever to feel like a mythic figure you should be willing to give them more superhuman abilities.
On the subject of rogue classes though, half the problem there is that rogues aren't that much of a combat class. Rogues are meant to be the sneaky guys who can mess with traps, bypass enemies, steal from enemies, catch them off-guard, disguise themselves, sneak into places others can't, talk their way past people, and generally be skillful sorts who show most of their strength
outside of direct combat, but most RPGs kind of limit all the gameplay to combat segments and make all the combat mandatory and direct combat so it's hard to make a rogue that really feels useful in the capacity of a rogue. That's why you often end up with rogues being the class that dualwields and often just hits enemies from behind.
Say, anyone got good ideas for abilities, etc. to make non-mage classes more interesting and awesome?