Hi,
To recapitulate the main points of the late stage of this thread (or what *should* be the main points

):
* Bless probably does better in larger parties than in smaller. If the party is too small, there aren't enough targets. Even if there are enough targets, the ones that do not make attack rolls gain no offensive benefit. As the party size increases further, it is possible to cast Bless on the attackers most likely to benefit from it. That can be a big deal. An analysis based on the idea that Feats don't exist and that all character turns have equal value when it comes to dealing damage is not relevant to the vast majority of games.
* Bless does more when enhancing important attacks, especially those that consume resources.
For example, there's something to be said to cast Bless in round 1 of combat, so that the Fighter can Action Surge with Bless. Action Surge is a limited resource; Bless helps to make it count. There's something to be said about pre-casting Bless on the Assassin so that his round 1 attacks hit and crit. Surprise is a limited resource; Bless helps make it count. Conversely, a Paladin does not have to expend spell slots on a smite until after a hit is scored; it still might be worth casting Bless on the Paladin but it does not act as insurance in the same way.
* The more difficult it is to hit, the more Bless shines. It is true that Bless adds between 5 and 20 to the percentage chance to hit, regardless of the AC being targeted. That is an average of 12.5. So if an attack normally succeeds X% of the time, Bless makes it succeed approximately X+12.5% of the time. (Any computer program that comes up with 10% is either deeply flawed or utterly broken.)
But to assert, based on this analysis, that Bless has the same effect for every AC is utterly and totally mistaken. Consider: Suppose I normally have a 10% chance to hit a difficult target, and that I inflict 100 hp of damage per hit. If I attack 10 times I have inflicted an average of 100hp. Then someone casts Bless on me. Now I have an average of 22.5% probability of hitting. If I attack 10 more times, I have inflicted an average of 225 damage. Bless has more than doubled my output! Bless has far less impact when attacking a target normally hit 50% of the time, increasing damage output by only 20%!
* Bless is great when attacking at disadvantage. Note that the d4 is not rerolled.
* And yes, Bless works very nicely with our favorite Feats.
* Finally, Bless does also help saving throws.
In some combats, and in some parties, Bless can outdo 3rd level spells.
Conversely, Bless doesn't do so well against creatures that are easy to hit, or when you do not fear failing a saving throw because the opposition does not have scary abilities, or in parties that don't have sufficient attackers. (Some of these combats can still be pretty dangerous! A single orc might be easy to hit, and have no abilities you need to save against, but a horde of them benefits from action economy and bounded accuracy... and if 1 in 4 of them is a 1st level cleric of Gruumsh willing to bless the frothing mob, they are even more dangerous.)
Anyway,
Ken