Well, there's a few things I want to say here. First, about just "having fun": yes, this is a game, and it should be fun. But your idea of fun isn't always the same as someone else's idea of fun. To those people, you saying that you don't want to use an axe as WAR because it's "not as fun" is you putting your own goals and desires in front of the group goal - something that's not a good thing to do. It's like if a pro basketball player is a "ball hog" and never passes to the other players on his team. It may be fun for him to do that, but it's not fun for the other members of his team, and he can expect that he'll be sitting on the bench soon. Plus, everyone's probably paying money to be in that party (through food and, for some jobs, NIN tools or ranged ammo), and you slowing down the party's exp/hour rate is really hurting their money.
Why can't people just have fun? I know it doesn't make you "teh l337" but, let people have their fun, and enjoy it with them.....
The bolded part is exactly why people don't do that. It's because they -can't- enjoy it with them. Your fun doesn't equal everyone's fun.
SMNs being main healers: Oddly enough, main healer is pretty much the only party role SMNs can really do. Healing magic, unlike most other types of magic, isn't very dependant on the healing magic skill. Using SMN/BLM and trying to nuke with BLM spells is bad, because you've got a half-level Elemental skill. But using SMN/WHM and healing with WHM spells works, because a half-level Healing skill doesn't matter as much. SMN also have an insanely high MP pool (I think a hume SMN has more MP than a taru BLM of the same level - or at least, it's close), and have Auto-Refresh. Plus they get five Clear Mind traits (WHMs only get four), and each trait comes 5 levels earlier than WHM. So, that's why SMNs can be main healer. Why can't they be a summoner, then? Two reasons - one, avatars are incredibly weak, and can't even be out all the time as it's a large drain on MP. Two, the only real redeeming quality of avatars, blood pacts, can only be used once per minute. So, you've got three choices as how to play SMN: Have an avatar out and have it melee, summon an avatar to use a BP, then dismiss it and rest until it's ready again, or use your sub's spells while waiting for the BP timer to cool down. It's fairly obvious which is better.
Of course, that doesn't mean SMNs are weak. They can be as good at main healing the tank as WHM (even with a PLD tank), plus they're able to buff the party using avatar BPs. And they can MB with level 4 nukes, or they can work as a skillchain partner for every SC (at level 5, a SMN with all avatars can open or close every single SC, as long as someone else can do the other WS in it - at level 30, they can do everything with all avatars except Fenrir).
About WARs using the right weapon: at low levels, there's not much of a difference - only 2 skill points in the 'dunes. Once you get into the higher levels, however, the difference begins to be noticable. Just look at a sniper's ring and you'll see how much people pay for just a few points of accuracy - and by level 40, you're missing out on 5 accuarcy by picking the wrong weapon. Also, if you use only a greatsword right now, you'll have a very difficult time getting an axe up high enough to use when it becomes really important.
Finally, here's a few things people say about playing the game "how they want", and my replies:
"SMN shouldn't be main healer, they don't even get healing spells without a sub."
-WAR is the only job to get Provoke, does that mean PLD and NIN shouldn't be tanks? WHM and RDM both get healing skill, does that mean both should be main healer?
"I'm only using this weapon because I'm going to switch to (insert job that uses that weapon here) when I get to 30."
-And I'm sure you'll make a good (insert job here). But right now, you're not a good (job), you're a crappy WAR.
"I just want to play the game how I want to. Can't you let me do that?"
-Oh, sure I can let you play how you want. In fact, I think I'll play how I want - and I know I want to party with someone other than you. Good bye. *either disband or boot that person, depending on if I'm leader or not*
Alright, so I don't use that third one often (I never have, actually). But I've been tempted to quite a few times.