So, if we use the analogy of D&D combat as a team sport, what do you think are the key positions?
I'm not well versed in team sports, so at the risk of going a little off topic I think I'll skip the analogy and talk about this in terms of the "classic" combat arms and other combat support and combat service support functions.
Naturally there is some overlap among characters and individual characters can fill more than one position, but I think the functions typically performed within a D&D party are as follows:
Infantry - This breaks down into heavy and light infantry with the fighter being the exemplar class in both areas.
Heavy infantry - This is the party's frontal assault and defensive force. It relies on a focus on melee weapons, so typical classes in this role are primarily Strength-based barbarians, fighters, paladins, and rangers.
Light infantry - Other infantry functions, such as scouting, skirmishing, and providing supporting missile fire, fall to light infantry. Dexterity-based fighters and rangers serve well in this role. Special forces, below, could be considered a sub-category.
Special forces - This covers a variety of specialized functions including scouting, information gathering, acquisition of high value targets/objects, and other activities requiring stealth and/or a high degree of mobility. This is the area of expertise for rogues and monks, and to some extent rangers.
Artillery - "Gunners" use ranged magic that goes beyond the range and firepower of non-magical ranged weapons employed by infantry and is the province of wizards and sorcerers,
fireball and
lightning bolt being the prime examples of the type of munitions being employed.
Combat engineering - Combat engineers use magic to modify the battlefield to ensure the mobility and survivability of their allies while creating obstacles for their enemies. All spellcasting classes seem to have access to spells enabling this role.
Military intelligence - This function collects and analyzes information. All spellcasters have some access to spells of this nature. Also, highly skilled characters such as rogues who engage in espionage and gathering human intelligence are performing this function.
Health services - Medical personnel are mainly spellcasters with access to healing magic, such as
cure wounds and
greater restoration. Spells like
mass healing word mark clerics as exemplars in this area.