Is Heavy Blade worth inhereting anymore?

I'm just gonna choose to ignore the first sentence of your question to shorten the post (I reply to too many similar to that sentence, lol).

Heavy Blade is good for units that have high base attack. With that said, however, many people would recommend not putting it in the A slot since it takes away from the possibility of other A slot skills like Life and Death, Swift Sparrow, Fury, Brazen, etc.

I'd personally just merge.

Not really. There are way better A skills these days and HB seal is a thing. I think you should just merge.

I actually thought about it, and there might be a case for strong (albeit, slow) hard-hitters, like Sanaki with a Blade Tome and Brash Assault > Desperation. They might benefit off of lowered-cooldown Glimmers, since it's not always garanteed they'll double.

Merge for higher score in the arena, or use him as aether fodder.

QP seal + galeforce shenanigans

like brave cherche

l gave it to my Nowi and refined her weapon for Atk as a meme. I regret it greatly so l'd suggest merging if you don't care about Aether.

QP 1-turn galeforce on fliers