Is there any methodology behind the variance in evolution levels of starter Pokemon?

Question

Most starter Pokemon first evolve at level 16, and then again at level 36. It would surprise me if this wasn't intentionally done for balancing reasons. Not too early that it gives you an excessive power boost, but not too late that you feel underpowered before it evolves. There are are, however, several Pokemon that break this norm by a few levels. Ivysaur, for example, evolves into Venusaur four levels before its Water and Fire type counterparts evolve into their final stages. All of the Unova starter Pokemon evolve into their second stages on level 17, one level later than what seems to be the average. The same applies to the Alola starters, though they also evolve into their third forms at level 34, two levels earlier than average.

So, why break this norm? Again, it seems pretty intentional that most of them evolve at level 16 and 36. Are the starters that evolve earlier known for being a little harder to use early game? I believe I remember some mention of choosing Bulbasaur making early game Gen 1 a bit more difficult, so could this perhaps be an attempt at balancing this aspect? I don't expect there to be any official mention of this phenomenon, just to be clear, though I'm curious how this aligns with things like type matchups of gyms and common types throughout the different regions.

Comments

Some are done to give starters with disadvantaged typings a fair shot in the early game. First one that comes to mind is Chimchar evolving at Level 14, so it gains Mach Punch in time for Roark.

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i do want to point out chikorita faces falkner and evolves later than cyndaquil, 16 and 14 respectively. i can't think of any logic behind any of the johto's starters evolution levels.

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It’s basically is just whatever gamefreak thinks is the most balanced

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I thought choosing Bulbasaur made things easier and Charmander made things harder

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It does

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There seems to be a very weak correlation between starter evolution levels. Starters that evolve later the first time (namely Totodile, Turtwig, and the gen 7 starters) are more likely to evolve again earlier, and every starter that evolve early the first time (namely Cyndaquil and Chimchar) evolves again at exactly level 36. There's also a weak correlation between the final stage's evolution level and base stat total, as starters that evolve before level 36 have slightly lower stats on average than starters that evolve exactly level 36. However, Monferno evolving and learning mach punch in time for Roark seems to be the only example of balancing starter evolution levels for gym matchups.

Also does this count as a Game Freak logic question?

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I intentionally worded this so it's not a Game Freak logic question, I believe, and I'll accept "there's no methodology" as an answer, given that it actually addresses how variance in evolution level does or doesn't affect the game in a way that makes it seem intentionally done for one reason or another.

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The question is fine. Pick a list of things that a sensible person might expect correlations for then go see if there is any evidence.