If the stated goal is to make Hotwire/Technician less versatile then why don't we simply split the classes role into two separate roles.
Have a Advance Engineer retain access to the Advance Repair Gun, and has access to Proximity Mines. However the Adv Engineer only has access to a Silenced Pistol for self defence, and does not have access to Remote C4 and only a single block of Timed C4
You then have a new class, whom I'll refer to as the Commando class, who has the Heavy Pistol, and multiple Remote and Timed C4. But does not have access to Proxy Mines. The Commando can either not spawn with a repair tool, or spawn with a 'free' repair gun that has a low ammo pool akin to buying a repair gun.
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The Adv Engineer takes on a defensive role of being a superior Engineer, but lacks any real staying power in direct combat. The Commando takes on the offensive role, being able to attack and destroy enemy buildings and certain strategic assets, and has some staying power with their Heavy Pistol/Remote C4.