Question about Balance/Consistency on GP Ultimate

For a while, I've been confused on this distinction on the difference between most global skills, and Gangplank's Cannon Barrage.

Here are the champions that have semi-global/global ultimates:

**

** = - only due to the pseudo-global attribute of his stealth.

Of this list, I will group into categories based on ultimate-type.

Global Linear Projectile:

Semi-Global/Global Teleport:

Map Movement + Damage:

AoE Damage:

Targeted Linear Projectile:

AoE Crowd Control:

Targeted Global Damage:

Global Heal

Why categorize them? Because in doing so, I point out an odd quality that GP's ult does NOT have with the rest of the ultimates with those it shares similar qualities. Let's go further:

1. The global linear projectiles, all of which are on ADCs, will generally have little to no warning unless you have vision on the caster. This is generally acceptable, given these are also the most skillshot-reliant of all the ultimates listed and can easily miss.
2. The teleports, which have specific criteria on their usage or do not actually allow full global range, will generally also have utility attached. All of these ultimates give a visual and audio cue upon usage that is global across the map and/or nearby characters whom it affects. In addition, none of these ultimates in and of themselves deal damage upon completion of the spell.
3. The ultimates that give movement + damage, which we will refer to as gap closers, will give an audio cue and/or a visual cue. Some use both. Sion and Kled are limited by the map terrain, Nocturne gives darkness but is only allowed to dash to one target, and Pantheon has a distinct visual indicator prior to his arrival on the targeted area. The exception here is Rengar, due to his pseudo-global nature of his stealth, but given that the assassin roster update will include his kit being reworked, we will overlook this anomaly as Riot has recognized that it's an unhealthy mechanic in the game anyway.
4. The AoE Crowd Control, Targeted Linear Projectile, Global Targeted Damage, and Global Heal are all significantly different in their presence/activation, but all are understandable as to why. Caitlyn's readies and targets before firing, and the projectile is able to be intercepted by allies. Karthus will hit all enemies but there is a 2+ second warning via a visual/audio indicator on your champion. Bard's is a projectile that has a certain speed with a ground indicator preceding its arrival. Soraka's is necessary to be instantaneous due to the consistent targeted nature of heals that are not AoE, as well as having an obvious visual/audio indicator accompanying the healing.
5. Those that are AoE Damage will generally do just that. But while they may differ in targeting mechanics, they will generally have fair warning for when they are about to make impact. The exception here is Gangplank. While Ziggs has a pseudo-global range + visual indicator of the area that will be hit, Xerath will have a range indicator emanate from his position as to the full radius that he can fire + only allowed to fire one small shot at a time, and Lux has a laser with an infared indicator for its maximum range + it is set in a linear fashion with the quality of also being AoE, Gangplank differs.

This is where I think Gangplank's ult is unhealthy because it betrays the consistency of global abilities that we have come to expect as players, both veterans and newcomers alike.** Gangplank is allowed full global range of his ultimate, has a massive AoE on its targeted area that rivals Ziggs' ultimate, has an instantaneous cast with no forewarning without already being within the affected area and having damage already make contact, and also slows all targets within the ultimate on top.** It doesn't unload all its damage at once, yes, but generally that isn't the focus of using the ultimate. The CC attached makes it already a frustrating ability to play around, as well as the instant cast nature of it without any forewarning. Also, to further make a point, all champions in this category frequently buy CDR. the mages naturally do, and Gangplank is allowed multiple items given the frequent CDR stats many items have now come to include in their purchases. Even if the argument against Gangplank's ultimate is that it has a significantly long cooldown, it is mitigated or even made moot by the inclusion of CDR to more items than ever before in LoL's extensive balance history.

What's more, Gangplank is the only champion that has the power to augment his ultimate multiple times in one game, with three upgrades each costing 500 Silver Serpents. The upgrades are: 1) Death's Daughter, which has a smaller AoE circle in the middle that immediately deals true damage and ALSO slows, 2) Raise Morale, where allies are given bonus movement speed whilst in the ultimate, and 3) Fire at Will, where the ultimate casts 6 additional waves to its already generous 12.

I am not one to say I have an idea of what should be balanced for Gangplank, and I admit that wholeheartedly. But if I were to cast any fingers at GP being an offender of Riot's design philosophy, it's that Gangplank's ultimate is quite possibly the most egregious offender to consistency of game mechanics that any global ultimate has within the game. Whether it means that the ultimate no longer deals damage effectively instantly, no longer CCs normally, nor longer is allowed global range, or has the AoE radius that it has, I don't know. The current PBE iteration at the time of this (PBE 8/9/2016) has a damage nerf on the ultimate, which is fine, but it still doesn't change the core mechanics that the ultimate still retains at the moment. But while the current thematic of Gangplank is very true to what it offers players who select Gangplank in champion select, the sheer nature of the ultimate and its core impact on any given moment after Gangplank hits level 6 means that there's essentially no counterplay to the skill itself, aside from using Flash (which already applies to all of the ultimates mentioned, so it's not enough). I could talk about his barrels also being problematic, but that's another topic that I won't emphasize now.

TL;DR - Gangplank's ult needs sufficient counterplay in his design. Numbers on damage won't be enough to remove frustration players have when playing against a Gangplank.