: Why are peanut allergies so much more severe than other food allergies? Based on my understanding of how adaptive immune responses arise, I would expect peanut allergies to be roughly normally distributed with regard to severity,

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To start, Peanut allergy is one of the most common allergens in the allergic population with 12 known allergen proteins.

four common food allergy superfamilies: Cupin (Ara h 1), Prolamin (Ara
h 2, 6, 7, 9), Profilim (Ara h 5), and Bet v-1-related proteins (Ara h
8). Among these peanut allergens, Ara h 1, Ara h 2, Ara h 3 and
Ara h 6 are considered to be major allergens which means that they
trigger an immunological response in more than 50% of the allergic
population.
Source: Mueller GA, Maleki SJ, Pedersen LC (2014). "The Molecular Basis of Peanut Allergy". Current Allergy and Asthma Reports.- wikipedia

Peanuts harbor 12 allergens and multiple isoforms recognized by the
Allergen Nomenclature Sub-Committee of... - Molecular basis of peanut allergy

Comparison
Compared to the other common allergy-causing food are : Eggs, Milk, Tree nuts, Fish, Shellfish, Wheat and Soy, which account for 90% (including peanuts) of the total allergic population -
American college of allergy, asthma and immunology

Five major allergenic proteins from the egg of the domestic chicken
(Gallus domesticus) have been identified wikipedia, egg allergy

Six major allergenic proteins from cow's milk have been identified wikipedia, milk allergy

Tree nuts
Hazenut: 13 allergen proteins
Wallnut: 7 allergen proteins
Pecan: 3
Almond: 6
Cashew: 4
Pistachio: 6

Science Direct

As implied from a long article, common fish species vary from 1-4 allergens..
NCBI - Fish Allergens at a Glance: Variable Allergenicity of Parvalbumins, the Major Fish Allergens

As implied from a tables in the article, common shellfish species vary from 1-4 allergens.. NCBI - Allergens and molecular diagnostics of shellfish allergy

There are four major classes of seed storage proteins: albumins, globulins, prolamins and glutelins wikipedia -Wheat allergy

Allergenic proteins from soy are named under a nomenclature decided by
IUIC, which is also responsible for numbering many of the proteins.
Proteins numbered by IUIC include:[18]
Gly m 1, a hydrophobic protein Gly m 2, defensin Gly m 3, profilin Gly
m 4, PR-10 Gly m 5, vicilin, a cupin Gly m 6, legumin, a cupin Gly m
7, seed biotinylated protein Gly m 8, 2S albumin These proteins are
recognized by the immune system as antigens in susceptible
individuals. As many as 8 other soy allergenic proteins are known. wikipedia - Soy allergy

Conclusion
Since there is no article directly correlating the food and the severity of its allergic reaction. It is safe to say that the number of allergens in the food has a significant relationship to the severity of the allergic reaction.
Notes
there had been studies regarding the relationship between doses and the reaction but with unpredictable results. Other studies emphasized the risk of doing human studies.