Concurred! Here is an additional logic driven "Test" on the "Area of Effect" (AoE) on the "Area of Range" (AoR) scale to examine effect radius and the amount of speed that would be required to move away. Before that, a quick review of the data which, contrary to initial assumptions is overwhelmingly in favor of Water Pokemon who learn nearly half of the moves on this list, and the ability to use Water moves to combat Fire, and he ability to use Ice moves to combat Grass, is unique scheme whereas all other starters counter only one.
In terms of the "AoI" of the moves the average radius of each is about 17 Feet in Range, and requires a minimum frame animation, or "Cast Time" of at least 2-Seconds. This means the earlier test of 10 Meters per 1-Second Speed correlation would allow certain Pokemon to later evade the majority of these AoE abilities as the collective Pokemon either run away (agile ones) or cast spells (the bulkiest of the Starters); from those that surpass the 17-Feet Radius Diameter Rule than we have 9-Moves out of the initial 26-Moves that could affect All Starters.
These moves are as follows: Lava Plume (Fire), Eruption (Fire), Surf (Water), Muddy Water (Water), Blizzard (Ice), Disarming Voice (Normal), Earthquake (Ground), Magnitude (Ground), and Rock Slide (Rock). From these 5-Super Effective on Fire, 0-Super Effective on Water, and 4-Super Effective on Grass. This means contrary to earlier arguments the water types once again have a significant advantage on the others; almost to a 2:1 Ratio which could lead to them being ganged up on, but then cross-fire would again damage those on the other teams.
Now then, in terms of the AoR of each of these nine abilities, the ones with the largest AoR are Eruption, Surf, Blizzard, and Earthquake so those will be considered the most lethal. A well-timed use of any one of these at the start (or more than one) would affect EVERY SINGLE Pokemon in the starting area as they fleed, with the exception of Charizard, Sceptile, Greninja, and Intellion who have the highest speed so at minimum would suffer only shockwaves and mild chills on the outside of of the area of impact. All others would suffer at least 30% dmg.
The Impact Radius of Earthquake would reach all four zones of shelter, but the trees would provide rooted defense to minimize.
The Impact Radius of Surf and Muddy Water likewise would barely reach the four zones of shelter, and be easily repelled by barriers.
The Impact Radius of Blizzard and Eruption are the largest of those remaining, and would also damage the stability of those structures.
Blizzard and Eruption would more or less deal lethal damage to every Grass Pokemon afflicted by both of these, even if escaping, with the exception of Sceptile who has a Speed Coefficient of ~27FT Per Second, and therefore could narrowly evade the radius of Eruption which is estimated at about 50-Square Feet, and be chilled by the Impact Radius of Blizzard which is around 75-Square Feet. This means that of the eight original Grass Pokemon, Sceptile is the only one remaining and could dash to Rocky or Jungle areas to protect against second case.
Eruption being 50-Square Feet WOULD reach the tree-line which was stated to be 20-40 Feet Away (depending who used) and that would also be intense enough to begin a blaze of the forest area, and partial blaze of the damp Jungle Terrain. The water types could easily put out the Jungle Types, and form a barrier to protect themselves, while the Fire Types who did flee the forest (and been hit by Earthquake) would suffer additional damage from the temperature in the air that would act more as 3rd Degree Burns. So farewell to all but Charizard and Infernape (and maybe) Typlosion who are at home in the forested areas or would be in the skies evading the blunt of the AoE Chaos.
Under these circumstances, we will now re-insert the above Logic Driven Arguments, and resume from the Argument 3 (which proceeded the Speed and Endurance Tests) that stipulates the remaining pokemon would all loath the Fire Types literally burning the world and team up, and that would leave three remaining water types and one fire type against a Grass Type... And of the remaining Water Types that are bound to win a three versus two fight, Greninja is the ONLY water type that learns moves that could sufficiently harm Intellion and others.
So my argument that Greninja wins stands the "AoE" and "AoR" as well as the "Speed" and "Endurance" and "Sociological" Tests.
All Adjacent
Lava Plume FIRE
80 100 15
Mind Blown FIRE
150 100 5
Searing Shot FIRE
100 100 5
Boomburst NORMAL
140 100 10
Earthquake GROUND
100 100 10
Magnitude GROUND
— 100 30
Petal Blizzard GRASS
90 100 15
Sludge Wave POISON
95 100 10
Sparkling Aria WATER
90 100 10
Surf WATER
90 100 15
All Adjacent Foes
Air Cutter FLYING
60 95 25
Disarming Voice FAIRY
40 ∞ 15
Hyper Voice NORMAL
90 100 10
Powder Snow ICE
40 100 25
Glaciate ICE
65 95 10
Icy Wind ICE
55 95 15
Blizzard ICE
110 70 5
Bubble WATER
40 100 30
Muddy Water WATER
90 85 10
Splishy Splash WATER
90 100 15
Water Spout WATER
150 100 5
Eruption FIRE
150 100 5
Incinerate FIRE
60 100 15
Cotton Spore GRASS
— 100 40
Razor Leaf GRASS
55 95 25
Rock Slide ROCK
75 90 10