If Holdo has been Ackbar it wouldn’t have really worked. The whole point of Holdo is to be someone we don’t know and don’t trust, much like Poe, someone without an established relationship with the audience.
Interesting point, but I’d argue that suits Ackbar’s character perfectly.
From the films we don’t know much about Ackbar. He’s a talented strategist. But the moment the rebels realize the shields are still on, Ackbar immediately says “retreat”. It’s Lando who encourages them to keep fighting. Even the trap line signifies he doesn’t like to have the odds stacked against while on the offensive.
In fact, when we think of Ackbar we immediately go to the Battle of Endor. Like Poe immediately jumping to Holdo’s victory. Poe/audience has high expectations to see the leader in a commanding role, but is disappointed by their retreating. This lines up perfectly for Ackbar, who we all think is cool but know little about.
I imagine people would just hate on TLJ anyway with the claim “they ruined Ackbar”, but personally I think he’d be a better choice.
You can’t really emote or act much in that puppet, though, that’s why he and other Mon Calamari are relegated to background roles.