So making Exploits and Extra Attack work together is good, in -theory-.
But what you're creating by having the exploits level up with the character is a level 20 Fighter who can throw 4 Cantrips out in a single action. Each dealing 5d10 damage to a primary target and other benefits.
Cleave, for example, would do 20d10 to your primary target and, essentially, 10d10 to your secondary target. Usable an infinite number of times per day. And as a bonus action strike them with the haft of your halberd for another d4 as an insult.
So it might be better to make them replace your entire attack action per-cast, at the scaling you've got going on, here. Or, if you want to give players multiple attacks, still, have the exploit damage scaling a finite value split among attacks. So if I make 4 Exploit Attacks at 20th level there's only a total of 5W damage that I get to split between those 4 attacks. One gets 2W damage, the rest I'm just using for the special secondary functions.
But what you're creating by having the exploits level up with the character is a level 20 Fighter who can throw 4 Cantrips out in a single action. Each dealing 5d10 damage to a primary target and other benefits.
Cleave, for example, would do 20d10 to your primary target and, essentially, 10d10 to your secondary target. Usable an infinite number of times per day. And as a bonus action strike them with the haft of your halberd for another d4 as an insult.
So it might be better to make them replace your entire attack action per-cast, at the scaling you've got going on, here. Or, if you want to give players multiple attacks, still, have the exploit damage scaling a finite value split among attacks. So if I make 4 Exploit Attacks at 20th level there's only a total of 5W damage that I get to split between those 4 attacks. One gets 2W damage, the rest I'm just using for the special secondary functions.