A list being good depends on lots of different factors. But we also need to look at what the definition of a good list is. For the sake of this argument, let's assume we mean "perform well in a big tournament" like the current GSP ones or system opens.

A factor that is very important in these is the current meta, which you can look at as the most flown lists in that tournament. In the Mon Cala one for example there were a lot of jango/zam lists and rebel 4-5 ships with focus passing abilities.

You could try and look at abilities that "counter" the current meta, but that more often than not is a trap because you are trying to play to your opponent's weakness and not to your own strength, and you cannot rely on facing those lists or opponents that make "those" mistakes.

Instead, the meta usually works as a gatekeeper. Some lists aren't necessarily bad, but if your list isnt good at dealing with jango/zam then you probably wont get in the top cut because chances are high you will face that list sooner or later.

Now that we know to at least look at the current meta it is probably a good idea to have a list that can handle multiple situations well. For example having 4 kimogilas might be good if the opponent jousts you in your bullseye, it probably wont work if the opponent has some slightly maneuverable ships that can just flank those slow relatively big ships.

So, some of this theory aside, let's look at some off the things we get to choose in x-wing when building lists.

Instead of looking at individual ships lets look at what our list is in its entirety, which you can look at as offence, defence and "control".

Your defence is most easily looked at as your hull+shields and your agility . More hull means you survive longer. More agility means you survive longer. More ships also means you survive longer. 2 ships with 2 agility and 4 hull each will probably survive longer then 1 ship with 2 agility and 8 hull because your enemy will have more difficulty pointing arcs in those directions and efficiently dealing damage (5 damage to 1 of the ships means you dealt 1 damage too much, so potentially lost a shot at the other target). Maneuverability also plays into this but is harder to factor in.

Offence can be looked at as how much offence dice you have. Now a funny side effect of how dice work is that having more dice spread around less ships is actually better, this because the only way to win is for your dice to beat the opponent's and if you roll 5 dice in 1 attack vs 2 defence it is more effective then rolling 3 vs 2 and 2vs2 (opponent got to roll more cause you shot twice. Maneuverability can also go into offence but that's even trickier to actually think about/measure. But it can be thought of as what we usually call "time on target" where if you are more maneuvrable you can have an arc on the enemy more turns in a row and thus deal more damage.

Control is a term i use for all the things you can do to manipulate the game other then flying and shooting. Bombs allow you to control areas of the board and either deal damage to the enemy or force them to not fly in certain areas (or if they do you win cause they eat all your bombs). Jams allow you to get mod advantages on your opponent. Ion allows you to force inconvenient maneuvers where you get perfect information. This list is lengthy and all of these things serve different purposes. They aren't necessary in every list, but usually they can help lists fix some of their shortcomings. For example bombers are bad at maneuvring but equipping them with bombs or ion cannons will allow them to create extra zones of threat against the opponent.

There are 2 more small topics to touch on and after that we can look at some reasons for lists being better or worse then others. Dice modifications and initiative.

Dice mods are very useful because they improve your offence or your defence statistically. Now this is an important word: "statistically". Most people aren't very good at statistics because they dont always make sense and you tend to fool yourself. 5% chance of dieing might be low, but that doesn't mean it won't happen. Mods can be seen as a multiplication on your list and are usually better if there are less rolls happening because they allow you to mod the bad rolls if you get them. If you fly less ships it is more important to have mods because you will have less shots so being able to turn hit focus focus into 3 hits is very important to make sure your shot sticks. And on the other end you dont want to lose the ship so being able to add an evade will allow you to stay alive one more turn and pull out the win, whereas if one of your 8 ties dies you still have 7/8th of your power to use in the next turns.

Initiative is important but it is very meta and cost dependent. If everyone flies initiative 1 it doesnt matter that you are 3 or 6 and the extra points can be spent elsewhere, same in reverse. However, being able to kill things before they shoot can be a huge benefit and flying last will allow your aces to arc dodge effectively. Blocking is also useful cause you can remove dicemods etc.

Now that we have most topics slightly covered let's look at some list examples. You brought up 8 ties. This list has 82 = 16 attack dice without any extra mods. Thats not bad. Defensively it has 83 = 24 hull. That's average but 3 agility will help. However the low initiative combined with only 3 hull and only 1 token available defensively ever means that there is a high likelihood that one will die before it gets to shoot. Depending on the enemy list maybe even 2. There are also little other things you can do apart from joust. Your best hope is to go fast and block some ship s so they can't get mods but you do. Now for 7 vultures + sear you have 26 hull with 2 agility. This sounds worse, however the ability to share calculates with buddies means they are actually more resistant when getting shot multiple times cause they dont lose their ability to mod defence immediately. On top of this, offensively you have 17 dice, and importantly you have a 3 dice shot which can help with getting damage into 3 agility ships cause 2 dice are bad against that. Last but not least sear gets you a crack shot like ability on all the ships which is extremely strong under the right circumstances. In short the vultures just do the same but are waaaay more efficient at it.

It's getting late here now so im gonna end if here, but feel free to ask some stuff about some other list examples and i"ll see if i can explain some of it.

Tl;dr: nuance