All the Gold Box FR and Dragonlance games from SSI and Stormfront used that formula of create six +1 or 2, including the original Neverwinter Nights which was the first MMO on AOL also based around the party of 6+ concept.
Even BG1/2 basically did the same with the heads up 7up, if you consider like Korax or Familiars in BG2 or other temp NPC types that are directly under the party's control. BG1 didn't have a summoning limit, it was more about whether your computer could handle it lol. BG2 had an overall limit at basically a dozen. I'm trying to recall if summoning a familiar occupied a permanent slot, or maybe it was capped at 11. But anyway there too, depending on how broad you want to think about 'the party' it was frequently controlling 6+ add ons. But yeah all the D&D computer games I can recall from the 80s and 90s were 6 and up. But in the late 90s early 2000s that changed when most games became either Solo focused, or solo + henchmen/followers, or group of 4.
Many of the older games that come to mind were for PCs. But I know most arcade games during the same period capped at 4 and still do. I can't think of any examples of a stand up arcade game with more, so perhaps there is something to that influence. After nintendo consoles kind of followed the arcade model rather than the PC one for a long time, except for a few titles in the jrpg lineage or until things like memory cards were more common. I think Dragon Age was probably a watershed for the 1-4 party. But I agree that it feels like its been 4 or bust for a while now. Like at least a decade or more