I genuinely thought you're criticizing the effect of evangelist dip on sailing, in that it allows bards to maintain lvl 30 song, while dipping 2 different dips (evangelist and loremaster) who give hard sail bonus. My bad. I honestly dont see what dirge has to do with it.
We can compare 20 bard 10 dirge, to 17 bard 3 evangelist 10 dirge and see how evangelist affects the setup.
Without evangelist, your ac will be lower, but it will be pretty decent. You will afford more con, int and cha when you dont need 13 str. You will afford a lot more feats when you dont need power attack, divine shield,, sf abjur and ad abjure. You will also have more spells between 17 and 20 bard.
With evangelist, you now have absurd ac, but longer wind up. Worth noting here that your extra ac is all dodge, and that bard already has enough ac that the best way to tackle it in pvp is through flat-footing - something divine shield doesnt help you with, at all. you are down 3 cl vs dispels which you can kill your feats to make up for 2 of the 3 as mentioned above.
The biggest upside for evangelist here is maintaining the 30 song, when having 10 dirge, but dirge at least gives undead summons full song. And if it wasnt for the lvl 30 song, 20 bard 10 dirge would be objeticely better, so it's fine.
Over all. Seems like a good design, but I will acknowledge that for someone who doesnt care as much about their CL and also wants domains for more hard sailing bonus, evangelist is a no brainer and is mostly only upsides, but that's ONLY in regards to sailing where traditional character stats are negligible. There's also no space for loremaster if you're a dirge singer which is the core of my confusion.
I also kindly ask you to stop trying to ridicule the stuff I say, when I only address the issue at hand and you deflect it to talk about me, Astral. Stop. It's irelevant here.