It also means that buffs that add a +1 or more are MUCH bigger than 3E and feel closer to AD&D in power. Three members of your party swinging melee weapons with Bless will be doing a LOT more damage over the life of the combat than that Cleric jumping in immediately and swinging a mace. It will also end the combat fast enough that you will spend fewer spells healing later.
This is an interesting statement. A Math One, I would say.
With the average damage of the rest of the party being around 45, adding average +2.5 to their to hit rolls results in 5.625 extra DPR. (Regardless of the enemy AC).
DPR of swinging a Mace with an average damage of 6.5 (1d6+3) depends on the opposition AC.
With enemy AC10 and higher, the Bless will be better all the time. But Bless takes resources, swinging does not.
Also, we need to take into account, that with an increase in AC, total DPR goes down, so we should look at the relative numbers, not absolute.
For example, against AC 13, Party DPR(mace) is 33.5, DPR(bless) is 34.9. A minor difference of 4.2%
But it gets better. At AC 17, DPRm is 23.2, DPRb is 28.1. 11.7% difference.
And the tougher opposition, the better. Against AC 20 it gives 23.8% higher damage output.
So while generally true - Bless is usually better than swinging a mace, but, against softer opponents, it might not be worth the slot/concentration.