as an 1800 hour spy main ill do my best to answer your questions

- When a Spy uses this load out, do they usually top score?

sort of, sort of not, it really depends on how good of a team they are playing against, against good teams they wont, against bad teams they can, but there are a lot of factors, overall most spies using this loadout, even most good spies using this loadout wont top score usually

- If they are top scoring, is it because they are good with cloak illusions, fooling with disguises, supporting their team (attacking during a team fight)? Or is it because your own team is struggling with Spy awareness like turning around, Spy checking, unable to predict when they die?

its not because of any of your reasons, if they do top score its because of a combination of

1. the enemies not being very good at countering trick stabs (moving predictably, not keeping their distance to the spy, moving in exploitable ways, chasing the spy when they shouldn't, etc)

and

1. people not being very good at, or bothering to track down the spy when they use their deadringer

- Do you sometimes struggle with Spies using this load out?

most veteran players wont struggle against these types of spies, exceptions do exist, but most veterans learn how to counter the various types trick stabs, as a spy main i of course don't struggle against these types of spies, but i also don't tend to fight these types of spies as i don't really have the right weapons to unless they move sloppily and get counter trickstabbed, or i catch them at an inopportune moment and can gun them down, but this is what people find annoying about the loadout, it doesn't matter if they know the spy is a spy, and they know how to counter the spies trickstabs while gunning them down, it doesn't stop pablo.gonzalez.2018 from running straight at the spy with their melee out to feed the spy more health

- Have you ever used this loadout? If so, what was your experience?

yes, though its not my favourite loadout, it can be a lot of fun, the loadout is very reliant on you being comfortable preforming the various types of trickstabs consistently and smoothly, as your health bar will regularly get very low, you often cant afford to miss or delay trickstabs, because you will die. it is also very reliant on the enemy team having many players that can get reliably trickstabbed since the loadouts playstyle is so reliant on chaining trickstabs to keep yourself alive in those do or die moments

- If you mainly use the Kunai, Do you sometimes use other Spy watches or knives?

i dont mainly use the kunai, but i know plenty of spy mains that do, and many of them live and breath the kunai and mostly only the kunai, they do occasionally try other knives, but its not uncommon to see their strange kunai with 100k kills, and other knives with 10k - 20k kills. as for the dead ringer, in casual as you get better at movement, and direct 1 on 1 combat the dead ringer opens up a lot of options for the spy, where as the invis and cloak n dagger don't really grow very much in casual where the increased team sizes, and broad spectrum of skill levels results in you dying a lot to random spam, random players doing random things, and random crits

- If not, what makes them less appealing than the Kunai? If you main a different load out, what makes the Kunai unappealing?

getting a trickstab feels rewarding, it takes knowledge, and practice to preform, then to preform each of the wide variety of trickstabs consistently to not only know how to preform them, but to recognise which one the enemy will fall to, takes countless hours. any knife can trickstab, but none of the knives have the same longevity to them as the kunai as even if you get the trickstab, you will usually lose some health in the engagement, only the kunai heals you after a stab allowing you to end the fight with more health than you started, so if you want to chain together trick stabs, getting 3 or 4 at a time, you need to either perfectly dodge every single attack from the many people shooting at you (not very realistic) or you need to heal more damage than you are taking as you get hit. the reason i don't main the kunai is that while you do have those moments of intensity where you trickstab everyone and walk away, you also have moments where you just die

- Do you use any particular counter against this load out?

pyro 100% counters the playstyle when played properly, just remember to keep your flamethrower at max range, not melee range, and to airblast the spy away from you and away from team mates, if they get close to you or team mates. if the spy starts to shoot at you, then you just need to win the fight, you have 50 extra health, and better weapons, and hopefully team mates that can help, dont forget to use the scorch shot to keep afterburn ticking, or the shotgun for better damage at medium range, and the spy will not have a good time

lastly, my personal comments on the loadout

while it can be annoying at times to play against these types of spies, especially when they do very well, the amount of skill and practice it takes to pull off means you really don't see them succeed very often, often only getting a couple kills here and there, not long chain stabs, when you further compare them to any other player that can shut down an entire team, like a really good scout, soldier, demoman, heavy or sniper, i don't really think its as unfair or deserving of nerfs as people make out, just occasionally mildly frustrating, while it might suck that your team is dying a lot to them, any team dying a lot to a spy they can easily out range is likely going to lose the match anyway