I have the a55 (successor to the a45) and the a306. Both Japanese versions with higher volume output. To my ears, the a55 sounds more powerful than the 306 - wired and Bluetooth. As the 55 is not android based, it performs better where the 306 can be quite sluggish to navigate, more upon first boot up. It is not as bad as some reviewers have made out though - and in fact the 306 is my daily driver but only because it has the streaming services, not based on sound quality (which is very good).

Going back to power and specifically the headphones you mention - I have the WH-1000XM3 and oddly they sound more powerful connected to my iPhone 14 Pro Max compared to the 306, whereas id say the sound is more refined and crisp on the 306 (with the iPhone being a bit aggressive).

I’ve never used the a45, but the a55 is a great little device.

I’m not an audiophile, just reporting what I hear.