Okay, so here is my rundown of the LLC characters from the viewpoint of a competitive PC player:
El Dragon: Not nearly as strong as he was in days past, he isn’t nearly as weak as some people would like to believe. He can function as a niche last-pick against a team sorely lacking the CC to deal with him, if played by a character comfortable on him. Rarely will you see him on Incursion, due to the lack of isolations he can achieve, but you may see him some on Meltdown since those isolations are possible, and there are fewer opportunities for him to be focused. Also, two new pieces of tech were recently discovered that improve his gameplay slightly: synergy between Sportsman’s Haute-Couture Kevlar and his level 6 helix “Hang Time”, and how his level 8 bicycle kick interacts with cancels into his skills (notably his ult). However, all this comes to a point: Phoebe can serve a similar function and do it more consistently. She has higher sustained damage (El Dragon outclasses her while in his ult, but not while outside), a more reliable initiation-escape combo, more mobility, roughly similar (if not better) chse, higher health, and the same damage reduction capability.
ISIC: Once the god of all character choices due to his AoE charged shot, ISIC has been brought down to earth with said AoE’s removal, the minion buff, and the axing of his perma-slow. While classed as a tank, ISIC is actually best played as a ranged DPS. His charged shot scales with both attack and skill damage, so building that on him can see him doing sniper-tier damage with a shot similar in behavior to Toby’s force-field shot. While he rarely sees play any more, this is more a factor of him not really fitting in with most meta team comps. He has all the tools to perform well: an escape, some degree of CC that he can obtain, a degree of tankiness from helixes and his reflecting wards, a sieging ult, crazy ranged damage, and a permanent wound. However, he’s just in a strange place in the current melee CC meta. He’s (nearly) got the tankiness to be a shield tank), but he lacks the CC options that tanks have, and doesn’t really have the presence to frontline like other big tanks (e.g. Montana) do. He’s got the ranged damage that other snipers have, but presents a large frame that other snipers lack, making it harder for the tanks to draw fire away from him. His ult is also really easy to shut down with all the CC that gets thrown around.
Kid Ultra: While he saw recent nerfs, KU still is a solid healer pickup, especially on Incursion. He can function similarly to Ambra in terms of healing and waveclear, but comes with higher damage and an AFK heal. He also has the late-game stun, that while severely nerfed, is still excellent at providing peel or canceling skills, and potentially providing the edge needed to win the late game. He also can stack crazy damage amp for ranged characters to camp on, or opt to not take the sunspot heals if there is another healer on the team, and instead stack 81% damage amp on a DPS for some nutty combos. However, he is a fat target with rather small animations, a small health pool, and a relatively large crit spot, making him a juicy sniper target. I personally would prefer KU on my team than Ambra.
Kleese: Complete garbage tier. He suffers greatly from “I’m a huge, immobile target” syndrome. He is good at setting up a camp and staying there, but has the easiest counterplay in the game: lob AOE into his camping spot, or hook him out of it. If Kleese is not sitting pretty in his rift network, he is dead. Kleese is only viable on certain team compositions that are filled with tanks to draw attention away from him and set up his overloaded mortars, and even then, if his team pushes up or rotates to the other lane, he is now vulnerable to instant deletion by common picks like Ghalt or common counters like Whiskey. He can only succeed if left completely ignored by the enemy team, and even then, he is hindering his team by being slow to relocate and being completely incapable of teamfighting.
Marquis: Very solid ranged carry, but only in the right hands. Despite the series of nerfs to his damage, Marquis still puts out serious hurt, and can absolutely decimate characters like Ernest, Kid Ultra, Miko, Ambra, Benedict, Orendi, and Toby, who pose massive crit spots and not much to do against him at range (with the exception of Toby). He also silently possesses some of the best wave clear in the game with his level 4 and level 8 helixes, as well as a nuke ult that is good as a finisher or a waveclear. His time bubble has a ridiculously low cooldown, and can be used to effectively block a choke point ad infinitum, or as an easy escape should someone jump on him. He also is the most reliable Shepard killer in the game, and almost always can kill Shepards between their overshield cooldown. However, he only rarely sees play, since he’s really only as good as your aim.
Phoebe: Phoebe can put out some incredible DPS, although she will rarely see much play on Incursion due to the lack of isolations and the prevalence of CC that just absolutely ruins her. I already discussed a good deal about Phoebe’s merits when talking about El Dragon, and it is worth mentioning that she is a frequent pick on Meltdown. She can get those isolations she is looking for, and has a much better opportunity to avoid CC since the teams are usually spread out. She also frequently will have a CC buddy running with her in Meltdown, so that they can set her up and hopefully absorb, bait out, or cancel some of the CC headed her way, and allow for her to carry.