Regarding long fights as the norm: no thanks. I'll take longer fights at intervals or end points, but not constantly. That'll become tedious quickly for me.
In terms of this, it does hurt the community aspect though. This game seems like the most active of mmos yet. Even more so than GW2 (which I don't really consider to be a mmo). You are constantly moving, nearly impossible to communicate while fighting. Add low hp high damage (quick) fights into the mix, and the game will basically be a whirlwind of action, at all times. Constantly moving.
This is the progression all mmos have taken since Everquest. Removal of downtimes, faster encounters, more active movement and a much more recognizable conning system (very easy to spot mobs you can/can not kill). It's very, very, very, rare to not know the outcome of the battle (outside of group content) these days, before you even attack the mob. So I actually agree with the tedium of todays fights, because there is rarely any risk. Zerg attacking (dying, respawning and trying again) a boss mob solo is not "risk", certainly doesn't register in your psyche as such.
DMK stated that it is better/more addictive to get smaller but more rewards. I have mentioned this before in the EQN thread. Sure, that might be true, if there was risk involved, as in risk vs rewards, but when you plow through content, the constant little rewards mean little to nothing as it is a +1, +1, ohh a +2, +1, etc grind of upgrades. This, to me, feels more like having a battle with the RNG to get lucky with the world loot tables than it is to find a mob and actively go after it for its loot and get a sense of accomplishment afterwards. I had a larger sentimental attachment to the first bag I managed to get in EQ than I had for any of my WoW loot in the little I ended up playing that game.
That being said, the way the combat system is in this game, they really don't have much choice of going the same route as everyone else. Fast encounters (30 seconds or less), more mobs and the danger comes from adds, not so much the abilities of one mob in particular (this seems to be the case too, based on the last twitch stream from the esper standpoint). Like every game since WoW onwards, it is unlikely that any mob 1/1 will pose any risk towards you at all unless it is much higher level.
Upside to doing this though is that general chat and such will be much better, as nobody will have time to type anything amidst all the jumping and dodging. I think mmos are growing more and more into massive single player games. MMO part is becoming more and more optional in "mmo"rpgs these days and faster combat is undoubtedly due part of this.
And no, this is not me saying I want the long tedious camps and kills of EQ. I would just like to play a mmo again where fights don't only pose a challenge when you make them so yourself (by going to higher level areas or group content). This has not been done since EQ as far as I know. There is rarely ever a risk of the unknown, and this includes the knowledge of "these mobs I can kill, these I can not". There is rarely a middle ground as well, due to the quickness of the fights that are common in games today, attacking a mob in a 1/1 is usually a known outcome before you even initiate the combat. So of course, quests saying kill 10x of a mob becomes boring, because it offers no challenge except the time it takes to kill them, where the only "unknown" is the potential of the RNG spitting out a green/blue/whatever color item from the world loot table. That is neither risk or rewarding. In EQ you could fight blue con mobs that if you made a mistake, you were dead, where you could push yourself to the limit, having to utilize mana gain items, etc. Add that element again to games, then quick fast paced combat might not be so problematic.
Problem as I see it boils down to - There was a bigger sense of unknown danger while camping the gnolls in Karanas staring at your spellbook, than there has ever been charging into a mob 1/1 in any mmo since EQ. Is that thumping an Elephant or a Cyclops? Then you heard a roar, and you quit med and desperately ran cursing the lack of having scribed the gate spell. And it is not like those fights weren't quick either, if the cyclops caught up, it would take roughly 2-3 seconds to kill me. Aside from running into world raid bosses, there are no equal level mobs that can kill you in 2-3 seconds or less that I know of in any game past EQ. However, if I was prepared, I could also kill the cyclops. Would take all my mana, and a lucky pet chain or two, but still doable. Not even sure what I am explaining here, but .... something is missing in mmos, and to me, it is the unknown. Faster battles tend to remove that even further, because it is very hard to design a fast encounter with an unknown outcome. Or I assume it is, because I haven't seen it done yet. Again, not talking group content, but just you by yourself vs a npc mob. Or to put it like this, ever gotten a kill X amount of Y mob quest where you even for a second thought "oh, I am not sure I can do this?". An equal level quest that is.
Tl;dr
Long fights without risk. Tedious. This needs to be removed.
Short fights without risk. Tedious. This needs to be removed.
And there we have removed all solo combat from any mmo since EQ... Think that was the biggest secret to EQ. A low functional limited UI that didn't give you the outcome before you even attempted something while having a system in place where you really didn't want to fail. So, like Draegan suggested, make some fast, some long, change them up, but easiest way to make it fun, is to make the fight outcome unknown while putting something of yours on the line as well as a risk upon failing. That makes encounters interesting no matter their duration.