everyone knows legacy delver so this shall be my example: your deck is built to reach its interactive spot before your opponents does. stifle FoW and daze are the typical small answers to keep the opponent far from developing their plan. BUT!! all of this is worthless without a threat to profit from hindering the opponent. so you need a threat and you need to grind this threat over a couple of turns to defeat the opponent. defeat is reached if you resolve a critical mass at a specific value (damage/ lifeloss in this particular example).
now what are the typical edh tempo engines? bob, fish, slibrary, tasigur, thrasios, rashmi, tymna, necro, edric, baby jace, yisan, pod, keranos, gitrog, ruric thar, zur, animar...
but thats different you say?!?!? no. the specific value might be different but the basic principle stays the same: reaching a critical mass at that value. now most of these cards give cardadvantage that if it reaches a critical mass might be engough to combo off even through counters or whatever hindrance there might be. the key element for comparison here is that most legacy decks dont abuse their life total and thus there is no resource thats attacked. its just reaching critical mass at a certain value with your tempo engine.
an important difference to aggro/sligh/burn decks:(still using legacy as example) even though these also aim to hit a critical mass at the same value their method to reach that goal is different. delver decks come with 3 basic cardtypes: 1. mana(lands), 2. tempo engines(delver/mongoose/whatever), 3. disruption (counter bounce removal ....). now you need to get access to a certain balance of these each game to have a fighting chance. burn comes with only 2 (for the nitpicky this might not be 100% correct but it doesnt matter if you can follow me to get the picture) basic cardtypes: 1. mana 2. threats. so its way easyer to hit the right balance here as there is a foctor less but at the cost of not having interaction when you might need so. another advantage is it doesnt matter if one or two threats get countered as you come with enough redundancy. just hit that critical mass to win.
so a tempoengine often isnt as redundant as threats in aggro decks are. in edh reaching critical mass via a tempo-engine can be translated via card-engines often. but how to translate threats from the aggro decks to edh? before delving any further lets sidestep into negative tempo-engines.
Smokestack doesnt give you resources to hit a critical mass at a certain value but it attacks the opponents resources. is it a threat like hermit druid in a combo deck? no. it doesnt represent emediate defeat if resolved and active. but its similarity to the tempo-engines is that it wants to stay as long as possible on the battlefield to do its thing. just inverting getting value to taking value.
now back to delver and burn: their similarity is the initiative. they both need to be proactive at a certain point and develop a threat to force the opponent into the reactive. this might force to change the opponents play to be reactive instead of developing their own plan to win. their threats though never mean emediate defeat for the opponent. only the last bolt/ attack that gets you to reach the critical mass symbolizes lethal value.
is an edh-tempo-engine a threat? not always. you might just let them have it and still combo off. of course a fish can get out of hand quickly so you cannot get throught their counterwall. same with a negative tempo-engine. you might suffer a little but in the end it doesnt matter if you can slip through with your combo to win.
so what is threatening and can be redundant in an edh deck? threatening but not emediately being lethal to opponents though( not a combo that wins on the spot)! not much as 100 singleton vs 120 life can not use the same tools/cards as you can abuse in legacy. but in my view there are some packages: reanimation + looting/entombing/tutors to get entomb can be packed enough to be redundant to get fast threats. be those negative engines like Sire Of Insanity, tempo engines like Consecrated Sphinx or a hybrid(praetor) like Jin-Gitaxias, Core Augur. when looking at this deck you also see lots of tempo engines, negative engines, symetric and asymetric tempo-decelerators. alone they never get a win. but if you resolve a critical mass of those you might win like the burn deck.
all in all i guess this is a really abstract picture but i hope this might give a brief understanding about my perception regarding edh and what can be aggro. a control player should definitly counter a lethal threat(combo) but cannot counter every threat(bolts or whatever in the legacy example). now a key about this is that in multiplayer if you counter a non-lethal threat the next opponent might just follow that up with a lethal-threat. i think there is a general understanding about this but not as deep as it could be. playing strangers often reveals them seeing threats wrong and countering a non-lethal threat only to lose to the next combo player. playing with regulars and talking about perspectives can change this to a better for this deck.