There is some confusion related to the strength and Life Rating of Angels.
It is said by Shi Feng (Chapter 2323) that :
"In terms of Life Rating, Archangels rivaled Dragons, while Higher Angels were slightly weaker."
It is also said in Chapter 2066, while Shi Feng was observing the various Angles Knights inside the hall Archangel Vatra teleported him into, that :
"Any one of these Tier 4 Knights could rival a Tier 5 human NPC in terms of combat power. The Knight Captain could even rival a Tier 5 Dragon."
Not even ordinary Dragons should be capable of rivaling opponents of an higher tier, only particularly strong dragons and divine dragons should be capable of doing so, let alone some random tier 4 Angel.
The Knight Captain is a tier 5 Angel. Perhaps he is a tier 5 High Angel. However it is later said that both Angels and High angels are slightly weaker than Dragons. The most reasonable explanation for this is that "Could Rival" only means "Are weaker but capable of fighting against without it being a one sided beating".
In the same Chapter this is also said about Archangels :
"The Angel race’s Life Rating was only slightly weaker than that of the Dragon race, and among Angels, Archangels were akin to Dragon Kings. They could even contend with Tier 6 Gods."
Archangels can contend with tier 6 gods, just like Fallen Archangels. However, why is in Chapter 2323 said that Archangels are only capable of rivaling Dragons? Also, in Chapter 2917, Fallen Archangels are said to be only slightly weaker than Divine Dragons. That also makes sense, however it doesn't make sense for Archangels to be only at the level of ordinary Dragons if they are only slightly weaker than Divine Dragons (The difference between Dragons and Divine Dragons is pretty high).
In the Chapter 2323 we see an Higher Valkyrie summoned by Anna fighting an ordinary Ice Dragon under both the effects of life curse and Shi Feng's Heavenly Dragon's Breath (The fragmented legendary ring which suppresses Dragons).
The Higher Angel is clearly stronger than the Dragon but the difference in strength is not incredibly high, still high enough however to keep suppressing slightly the Dragon even after Heathwaite had gone berserk.
The most reasonable explanation about the Higher Angel and Heathwaite's power levels is probably something like this :
Heathwaite(Normal) = 4,9(Apex of tier 4) ;
Heathwaite(Life Curse, Suppressed by SF) = 4,6 (Upper stage of tier 4)
Heathwaite (Berserk, Life Curse, Suppressed by Shi Feng) = 4,75 (Upper-peak stage of tier 4)
Higher Angel = 4,8(Peak Stage of tier 4).
It is possible to assume that Fallen Angels do have a similar strength to their Angelic counterparts.
We only got to know 4 different Fallen Angels Through the story : an Higher Fallen Angel (Serena) and 3 Fallen Archangels.
In Chapter 2897 this is said about Fallen Angels :
"Fallen Angels possessed Life Ratings close to those of Dragons. Meanwhile, Fallen Archangels’ Life Rating surpassed even that of ordinary Dragons. They almost rivaled Divine Dragons."
This statement is confirmed when 2 Fallen Archangels break into the various superpowers' conference in chapter 2916 and they single-handedly manage to suppress and kill almost every tier 5 player in there, it is particularly remarkable when Shi Feng and one of the Fallen Archangels fight and stall each other : Shi Feng was equipped with various fragmented legendary and 2 legendary pieces of euipment and he was wielding 2 top tier legendary weapons (Not one, two top tier legendary weapons, remember that just one legendary weapon should be capable of allowing someone to fight against opponents of an higher tier, even if that's an exaggeration we are talking about 2 legendary top tier weapons, in other words Shi Feng already had the power to contend against an ordinary Tier 6 god-ranked player that wasn't wielding legendary weapons too).
So, in summary :
Chapter 2066 :
Tier 4 Angels can rival tier 5 NPCs (unreasonable):
Tier 5 Angel/High Angel can rival tier 5 Dragons (It's reasonable for an high Angel to be able to contend with a Dragon, however it's later said that both Angels and High Angels are weaker than Dragons of the same level and tier) ;
Tier 5 Archangels are capable of contending with tier 6 Gods (Reasonable assuming that it's a God-ranked player without legendary weapons. Also, it is later said that Archangels are only capable of rivaling Dragons ; However it is then said [and shown] that Fallen Archangels [presumably Archangels too] are capable of contending against lower-end tier 6 existences)
Chapter 2323 :
Angels are slightly weaker than Dragons (Reasonable) ;
High Angels are still slightly weaker than Dragons (Not very reasonable, however it is shown in battle that this is true , maybe that particular high angel was drunk) ;
Archangels are as strong as Dragons (Unreasonable, and it is literally said [and shown] later than Fallen Archangels are just slightly weaker than Divine Dragons)
Chapter 2897&2917:
Fallen Archangels are said (and shown) to be able to contend with tier 6 gods (reasonable assuming that those Gods are on the lower end of tier 6, sure enough the Goddess Sharlyn was able to overwhelm 2 Fallen Archangels simultaneously but Sharlyn is probably a pretty strong Goddes considering that she wasn't even at her full strength during that battle).
Taking into account the various things that were said about Angels and Fallen Angels, the following appears to me as the most reasonable power list for tier 5 Angels :
Angels ≈ 5,75
High Angels ≈ 5,85
Dragons ≈ 5,9
Archangels ≈ 6,15
Divine Dragons ≈ 6,3
Sharlyn (When fighting the Fallen Archangels) ≈ 6,5
Shi Feng (Tier 5, with 2 legendary weapons) ≈ 6,1