I'm not going to complain about the AP mine cluster shell. They are much smaller mines after all so I think thats fine. The problem is with the AT mines. That should not be a "cluster" shell.

There is an 155mm artillery shell with nine AT mines IRL but those mines are very very smal and have some drawbacks that we don't have ingame. For instace: They only work on soft surface. Try to employ them on asphalt or concrete and they are crushed on impact and are of no use.

artillery
advantage : powerfull shells + high firing range
disavantage : weakness defense + slow motion + innacurate

So this is normal (for me) that it fires 8 mines as it is really innacurate.
Moreover as you said, thoses mines are very small, and a Scorcher don't have so many mine rounds.

If we start to nerve this, we'll have to nerves other shells, then nerves everything for a final flat casual game. This is the role of the mission maker to make the game fair. Well this is my opinion, and this is why i voted NO. :)

The only unfair thing that i see : when mines fall near ennemy AI, AI doesn't react, like "oh, it's raining, no matter..."

This is not just about balancing, this is also unrealistic.

I would be okay with it if they did not work on hard surfaces, like runways.