I'm sorry this is very long as I am very wordy.
1. Its depend on what job you have and at what level you are. On the one hand, for melee, in the end having a static party will definitely be worth their time (less time lfg, more time exp). If you're one of the so called "desirable" jobs that find a party no problem, you might be less inclined to wait around for a static party when you reach the 50's. I'll tell you why, at lower levels where some people don't know how to play the game, having a set party will breeze you through, but when you get to the 50's where most have become accustomed to their job, pick up parties tends to move these "desirable jobs" faster than a static can. I will explain the different type of static parties later and why some people aren't willing to wait.
2. There are bad players everywhere at any levels and usually their reputation precedes them. I've partied with one warrior in full AF at 61 wearing bastokan ring wanting to tank Peryton in the valley.
3. Yes there are statics that do other stuff besides leveling, but these people are usually good friends and belong to the same linkshell. There are static parties that are formed from linkshell members or real life friends and then there are pick up statics that are formed from meeting random people with the needed jobs. The latter tends to break up faster. Good loyal people who you enjoy being with will causes you to wait for them to level with you vs. pick up parties with no strong bond where individual don't have the patience to wait for others.
4. This is the downfall of statics, having to wait for everyone to be around at the same time. If the static party find replacement for a player at lower level, he/she will fall behind by the time they get back and will be discouraged. HOwever, at later levels when exp jump to 30-40k a level, having a replacement for one or two sessons is OK.
Rarely will 6 members be able to get online together to party for days at a time unless they are hardcore players. What I usually see forming now is a partial set party. Meaning 2-4 members agrees to level with each other and pick up the remaining 2 people. These works best when the members of the static have all the available jobs to formed the core of the party like tank, healer, refresher etc.
Most people will say, "I have had good experiences with my set, don't know what you're talking about". But take a look at it this way. By the time you get to level 65 you have only completed half the exp requirement to get to level 75. That means if you have good experiences with set at lower levels, you might not be able to handle the week long grind to get a level vs 2-3 levels a day at lower levels in a set. This will causes some sets to break up as well since it look like it takes forever.
Having a static that will reach 65 is another matter. I've been in 4 set parties since I've played for Bard job alone. Surprisingly I wasn't the first to leave because of slow exp because people won't show up to party or what not. Usually the paladin or the whm seek greener pasture and break the set. I've sat back and waited 4 levels in the 50s so members of my set can catch up only to find out I can only level like once a week with them, so I unfortunately have to bow out.
5. The exp grind will get so bad after Genkei 5 at 40k + a level that leveling will became less of a priority. Usually by the time you reach 65 you are occupied by other things that are much more enjoyable than daily exp grind that some people might level 2-3 levels a month. Alot of people will quit after 60 and go back to another job because they couldnt' handle the jump to 20k per level. The remaining players will probly still be able to grind to 65 and then experienced a big slow down.
This is where static sort of play a role. The player pool will be so small that even as bard or whm you can be lfg for a bit. Camp grounds usually can only accomodate 2 parties at most. With a static that is willing to put the time in to leveling you can pretty much go out and wreak havoc, as a single player lfg, it gets a bit harder, even as bard or whm because simply most of the time there aren't enough players to make a decent group. Plus exp grind after 65 will be 30k +
Right now at level 71 its the time I wish I am in a set as to not have to waste time lfp. A well oiled static will pull in more exp than a pick up party that is established. A static with similar minded individual with similar schedule and playtime will go very far and make experience with the game very enjoyable. A static where people are invited simply because they are the job that the static needs and haven't had the time to build a bond with other players will fall apart quickly.
I've leveled throughout most of the 60s with 2 other people, a thief and a war/nin. Usually we will pick up the rest of the group and even that take some effort, but at least we already have half the party. Most of the time past 65 you will end up leveling with the same people over and over, so most single players winds up becoming a sort of un official static anyhow.
So finally, in conclusion, IMHO statics between level 11-50 will go by very fast. Static 50-65 will probly experienced alot of breaks up and replacement if the party doesn't have a strong bond. In the 50's there will be alot of interruption due to AF and genkei and what not so Statics are also harder to maintain if you are not in the same LS.
Statics after 65-75 will be excellent only if the party have enough time to level alot and alot. 65-75 make up 50 percent of the game's leveling grind and where you get alot of wonderful toys to use. Having a static in the same linkshell at this point works because everyone have the same LS things to do and can level together after LS stuff or off days. There will be alot of LS event at this level as most of the desirable gears are rare/ex and require LS help as well as missions, camping monsters helping lower levels in LS and junk.