Yes, I’m aware of that option. The problem is, it means the GameMode is going to have to contain the objective-completion framework for EVERY level. If each level has, say, 10 unique objectives, and I want to handle each of these one-offs via a Custom Event, then with 6 levels I’d need 60 events in GameMode’s BP, with most of them going unused.
I’m not saying it’s unachievable that way, I just hardly think it makes much SENSE. The process of completing objectives is generic to the game mode itself, and the specific rules which govern whether each objective is completed are specific to the level. To my mind, that means that Classes which can potentially influence objective completion should report what happens to them to the Level BP (e.g. “My death is listed as relevant to Objective1 and I have died”), the Level BP should translate these notifications into objective completions (e.g. "All 3 actors which must die for Objective1’s conditions to be satisfied are dead, so Objective1 is completed) and then pass that information along to the HUD, SaveGame, and/or whatever else needs to know that an objective has been completed.
Allowing the GameMode to handle it directly is an option, of course, it just means that something which is not generally unique from level to level must either be changed slightly to suit each level or must contain within itself the logic applicable to all levels, neither of which seems like the “Right” way to do it when there’s already a perfectly good level-specific BP class right there (being the Level BP)
EDIT: If you ever played Tony Hawk’s Pro Skater you may understand what I’m talking about. Each level generally has the same “rules” for counting down time, calculating score, etc., but in one level maybe you’re supposed to grind on 3 fountains and in another level you’re supposed to frontflip over a schoolbus, right? Those objectives have rules which are unique to the map itself, though the fact that their conditions have been satisfied and they can be crossed off the list, as well as the visual indicators of their completion both in-game and out, is something which is not unique to the level. So the level needs to handle the “rules” of each unique objective in a way that can convert it into a more generic “completion!” notice for the overall game mode itself. What I’m doing is basically that.