If someone is playing for the first time or just casually, they should just use whomever they want. There's plenty of experience to go around and a handful of good prepremotes that can carry you even if you mess up horribly (in most games, anyways). Archers suck in the vast majority of FE games, but if someone is having fun using them on a casual playthrough, why stop them? People have fun raising trainee units despite their massive cost (and often underwhelming final stats). The great thing about FE games is that they can accommodate many different playstyles, even suboptimal ones.
Nowadays I have a lot of fun trying to play efficiently. But I also used to have a great time only promoting at level 20 and maxing units and all that jazz. Most of the advice like, "never use archers" or "never use armor knights" or "don't bother levelling anyone up but Seth" are usually true for efficiency runs (especially on higher difficulties), but hardly applicable for a first-time player who just wants to see the story. And to be honest, if I was a new player and people told me to not use certain characters I liked, I think I'd enjoy the game a lot less.
Exactly what I was trying to get across. Like, the high efficiency ranking runs suck. They really do. Sure, it's fun, but you don't get to take characters you like all the way along and strategize on your own time to do whatever you want to do however you want to do it, you get to change maybe a few turns across an entire run because you prefer a valuable or an extra weapon and can lose turns elsewhere. A ranking run is resource management at its core, efficiency never melds with what you like, and in a game series increasingly about its characters more than its gameplay, it's not a great idea to bring those considerations in, in someone's first game...That's the way I feel about it, anyway.
Even further, after FE7, you have "unlimited levels and stat ups" in FE8, bonus EXP bonanza in FE9 and 10, Awakening and Fates don't have EXP caps and stat-ups are easy to come by, further creating an open-ended experience, so even the efficiency runs are pushed deeper into mechanics where, again, the average new player won't tread.
I personally love efficiency and ranking runs, I love playing on the hardest difficulty and doing it as fast and loose as I can, but at the same time, characters are what endear people to the games, and cutting a bunch of them out because they take too long or too much effort for menial payoff...I can't agree with that.
And all of that is before support conversations, where much of the world building and characterizations come into play.
