Diablo 4 has been out for a bit more than a year now, which gives enough time to reflect on Blizzard's design philosophies regarding group play and take a look at the current state of solo vs group play balance in Diablo 4. While many changes have already been implemented for quality-of-life, there's still quite a ways to go — we're exploring the current state of Group Play in Diablo 4, and diving into potential solutions to common problems the community faces.
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Ex-Lead Systems Designer David Kim gave some insight into Blizzard's design philosophy for group interactions during an interview with Rhykker at BlizzCon 2019. The developers wanted to provide options for players who were looking for a more support-oriented playstyle while also making sure that «everyone is playing the game and fighting the monsters», specifically mentioning skills that would directly interact with monsters during combat, e.g. skills that allow players to pull monsters together. It is likely that Blizzard wanted to keep effects that interact with other players to a minimum, seeing how it affected group play by having pure support builds play a big role in the group meta and made solo play inferior in many regards in Diablo 3.
Blizzard seems to take a more cautious approach with Diablo 4 when it comes to group synergies that affect the balance between solo and group play, which is supported by Lead Class Designer Adam Jackson during an interview with wudijo at BlizzCon 2023. In the interview, Adam Jackson asked the community for feedback on skill interactions between players.