The proposed change of draining orbs does very little to address the almost instant, no aiming required and crutch-like, tactical advantage given by the orblord setup. Sure, it specifically addresses sitting on the orb at full armor, there is just a loophole around it: you would just have people avoid sitting on it, instead sitting right next to it and stepping into the orb when taking damage to avoid wasteful drainage.
The proposed change does not address the way how the orb is used in combat to effectively gain a huge effective armor advantage. If you balance the game by small armor differences like some mechs having 355 armor and other having 320 armor and one is being seen as squishy and the other as having "too much armor" (at a 35 armor difference), what do you think happens when you introduce an item that gives 170 armor over a short duration?
Just gut the in-combat healing gained by the orb and especially multiple orbs (make it only repair at the rate of a single orb). Why?
Almost every healing mechanic in the game is affected by shooting the healing target. Healing gained by 'C' gets interrupted for a short time after taking damage, Technician's beam's healing becomes weaker for a short time if the patient takes damage and the self-healing from the vamp beam becomes weaker if you take damage, Brawler turret mode's healing drops considerably for a short time after taking damage. Reconstructors get interrupted by taking (and annoyingly, dealing) damage.
This does not apply to the Repair Orb or Armor Fusor. While the Armor Fusor effect is powerful on mechs that have a lot of armor, extending their longevity, it does not let them survive through high DPS or let them to heal to full in a few seconds from near-death (at least on the PC version with healing divided over 20 seconds). The Repair Orb, even with its 2 second delay upon throwing, gives a considerable boost on surviving while in combat, being comparable to a Technician heal beam. Even more so with internals that almost double the healing per second, making it more unlikely to die while the orb is actively healing or with multiple orbs that multiply the effect even more. Even the Green Beam does not heal as effectively as internal boosted multiple orbs that let you survive an attack even if you had dropped to a low armor state.
If you gut the in-combat healing by the orb to say, 15 armor/second base value (still affected by internals) for 2 seconds after taking damage, you could still boost that to 28.275 armor/second (for 1.885 modifier I assume with +45% Adv. Extractor and +30% Adv. Repair Kit). After a 60% damage reduction, a Vanguard in turret mode could effectively reduce incoming DPS by ~70, not counting flankers and splash weapons (especially TOW and GL), it'd still provide somewhat of a boost to the current Vanguard, but not over the top, and certainly something you wouldn't try in every scenario (one trick ponies suck).
Outside of the Vanguard example, the orblord kit would mostly be useful for quick repairs out of combat near the frontline. A Brawler (another orblord kit user) could throw out an orb behind cover while waiting to cool off weapons, extracting the orb out by the time the weapons are completely cooled off.
The repair orb would still be effective out of combat. Just like every other form of healing. It would still make repairs faster, let you repair decent amounts of armor while having access to the radar. Dropping an orb on top of a death orb for extra 290-377 effective armor should not be the grand strategy in open combat.