Today I wanted to take a quick moment to talk about two terms that get bandied around a lot when talking about games, how they work, and how they feel. Players are often annoyed by feeling weak. GMs often struggle with players being too strong. But in my experience when talking about those problems what is actually happening is it isn't about strength or weakness, but about agency. So let's go into both real quick, because they'll be important for other conversations.
Power, strength, or many other words it is called is about actual mechanical power. In D&D 5e the Fireball and Lightning bolt spell have more power than other 3rd level spells on purpose. The designers felt the spells were iconic enough and should have that extra oomph so it is there. Rangers, on the other hand, by a fair number of folk's opinions, are weak and tend to fall behind other classes in terms of damage output and other things they can do.
Power tends to sort itself out. If you see all the power gamers in your circle going for the same options, odds are it is the strongest. If you see a lot of people avoiding or constantly trying to fix something by buffing it or finding more uses for it, odds are it is weak. As a GM I tend to not worry about power too much. I can tailor my adventures to challenge anything - be the PCs ridiculously strong or ridiculously weak.
Agency on the other hand is often mistaken for power - and a type of power is involved - but is ultimately more about meaningful choice. How much meaningful choice does a person have? That's how much agency they have. Mechanically speaking a Rogue tends to not have a lot of combat agency. They have a very powerful sneak attack, but - with the exception of clever players or specific set ups - there sin't much meaningful choice to how a rogue works. You just apply your sneak attack damage to the right opponent and let the power do more.
Wizards, Druids, and other spell casters on the other hand have a lot of agency in battles. Spells have powerful effects some of which damage the enemies, some buff allies, some debuff enemies, some protect people. What a spell caster chooses to do, what resources they choose to spend, can be very meaningful. This increased agency is also why some people don't like playing the classes and why it can be harder for someone to run two characters when the one they don't normally run is a spell caster.
However, Agency, or lack there of, tends to rear its head in other ways in games. Namely, if a GM doesn't allow the PCs to make meaningful choices that effect the story/what is going on for a long period of time, the game is considered "on rails" or the GM is "railroading" and this is a bad thing. Some railroading can be ok - adventures have to start some how - but GMs who keep player agency very low for most ofthe game, tend to have less happy players. Or at least less interested players.
The More Important
Of the two, I feel Agency is the one a GM wants to be more aware of. Yes, you should know how strong your PCs are, but you should be focusing to make sure you maintain player agency. A game with high agency but weak PCs can be a lot of fun. This can lead to more meat grinder games, where the players have to pull every trick in the book to stay alive. Black Trenchcoat Shadowrun is like that, and with the right group that is some of the most fun you can have around a table.
High power high agency games can end up with the PCs being the movers and shakers of the world, which itself can be a lot of fun and get games that run like Lord of the Rings, or maybe Game of Thrones depending on how bloody it gets.