Which class has access to the best ‘stay at home’ adventuring methods?

Assuming a 20th level character, which class would allow them to remotely assist a party of adventurers without ever leaving a well-warded personal sanctum? In 3.5e/PF, there existed a plethora of spells mostly based around the Wizard to support this kind of ‘off-site meddling’ but I know less about 5E and what Wizards and their ilk can accomplish there (especially at higher levels).

For the purposes of this question, assume the following;

  • The character is completely unwilling to leave their sanctum unless they have some inherent way to cheat death that is 100% reliable (paying a powerful cleric to resurrect you after X time doesn’t count for our paranoid and suspicious protagonist).
  • Class features that are mobile (such as Familiars or Animal Companions) can leave the sanctum, as can summoned or bound creatures.
  • They have intentionally chosen their class and even found some way of acquiring reasonable magic items towards this goal – they are a purpose-built ‘remote assistance’ character.

‘Best’ is not simply damage-per-round but overall quality of assistance – a battery of divinations doesn’t directly do damage but does allow the party to bypass encounters, effectively doing all the damage of the enemy hp of that encounter. Remote healing is not damage but can keep party members alive to do more damage, so on. In this case I am not looking at any specific character level for the party being assisted, but rather at spells, techniques, or class features that would apply to the widest range of parties successfully. Consider this less ‘bob stays at home and still helps the party’ but more ‘Mordenkainen’s Magical Assist (MMA) Incorporated’.