The issue is that the bias is extremely unpredictable and appears largely latency dependent. The tunnel game itself likely has no bias, but latency compensation does.
The solution to the aggressor advantage is to take another look at how the tunnel game and latency compensation interact. Then, once the underlying mechanisms are sound, the possibility for contextual biases from equipment could be looked at.
That's almost certainly how it's implemented. There is no way Frontier is intentionally biasing the interdiction minigame toward the attacker; it's a side effect.
Latency compensation, which is mandatory for a game where people on the opposite sides of the planet are expected to be able to reliably instance, favors the 'shooter'. In any exchange the attacker's perspective takes precedent, even when all involved are attackers. Everyone sees a slightly different scenario, but if you see a hit on your opponent, your opponent is hit, even if this would be impossible from their perspective. The tunnel game is more one-sided, once it starts it has a fixed aggressor and a defender and the the former takes precedent to prevent lag from being a shield, or just because that's how it works everywhere else. Unfortunately this means the aggressor sets the pace and their wiggling can only be reacted to, often far too late, if pings are high...it's how the tunnel game can end very abruptly for the defender, even when it still looks like they have a chance from their end.
Now I don't know the specific details of Elite: Dangerous' latency compensation, but I know it exists (I've experienced all kinds of shadowrams and desyncs that are highly typical of it...and the fact that I score hits on other CMDRs when I see my shots land, no matter what they see, is hard proof of it), and it there are only a few rational ways it could have been implemented. Of course, in a peer-to-peer game, everyone is a client and a server (though instance hosts get extra server duty), but this doesn't change the basic aspects of what latency compensation is or what it's doing.
Some information on latency compensation, both in general and specific implementations:
developer.valvesoftware.com
Source: https://www.youtube.com/watch?v=2kIgbvl7FRs
Source: https://www.youtube.com/watch?v=Fn269cI3hd8
Source: https://www.youtube.com/watch?v=6EwaW2iz4iA
Source: https://www.youtube.com/watch?v=xyCQtUFOJmA