Yeah I think you're onto something. In general shorter runners have more success in the marathon. I know some people deny this, but lighter is better in distance running, as long as you have enough muscle mass to be strong and enough fat stores to be healthy.
Really petite athletes like Helen Obiri and Peres Jepchirchir while lean, aren't extremely thin yet still have low body weights since they are so short. East Africans tend to be shorter on average than Caucasians, so you see more taller marathoners from the U.S. and Europe. I think these taller runners try to compensate from the added bodyweight to to height by being too thin, which introduces a ton of health and injury risks. While shorter U.S. runners like Dakota Lindwurm and Emily Sisson skirt these risks similar to East African runners, taller runners like Fiona O'Keeffe and Molly Seidel are 5'7" and constantly injured. Eilish McColgan is another example. She's 5'11", 117 lbs, and constantly injured.
One exception is Sifan Hassan, who is also 5'7". The difference with her is that she naturally has a very narrow frame, which is common among Ethiopians. While she is thin and light, she has enough body fat to be healthy do to her genetics, unlike the Caucasian runners who are a similar height and weight.
You mentioned Emma Bates as well, who is 5'4". She's a bit taller than Sisson and Lindwurm, but she seems pretty healthy by maintaining a lot of lean muscle mass. It seems like she relies on having a big engine and fueling more frequently during marathons (I think she says she fuels every 5K). It's probably also why she has more success on hilly courses like Boston, where she uses her strength and energy help her drive up the hills instead of trying to be in an extremely energy efficient rhythm on a flat course. This is probably the best formula for taller Caucasian runners in the marathon