Something being rare should not mean finding it is confined to areas under control of a very small amount of people, that will just unbalance things more. Specifically gamma, where bases keep the "natives" safe from having to deal with PVP and where observers are plentiful and easy to kill. It all sounds too self-serving.
Also, why should new content be restricted to a few "elites" being able to control supply? That would have NO value to the game whatsoever!
As for better mk3 seed mechanics:
1. Make it a very rare drop in artifact scanning on BETA, where everyone with balls can access it and still have to do some serious effort to find them.
2. Use the existing SAP mechanic. I don't like this option as it really is free candy. Tying even more game balance into the broken mechanics (my personal opinion) of conquerable structures seems bad to me.
3. Make multiple mk2 CTs convertible to a Mk3 one. But please make this vastly inferior to say the quality you get with artifact scanning. Exposed activity should be rewarded!
Now to the core of the idea, are the Mk3 bots as described desirable?
I think adding glass cannons just ads a ton of scenarios that scream exploit. It also promote blob fights where one side is sure to win regardless of tank and throw out possible interesting fights and tactics.
For PVE the whole proposal is bad, spawns that need little tank are so easy, the firepower would go to waste. And those that are hard, require the tank. A reverse proposal might work for PVE tho, more tank, less damage. Allowing players with less accounts then me to take on harder spawns, be it more time consuming.
A better idea would be to make mk3 speed and range specialists (detection + lock + optimal) with moderate dps, mediocre tank and very easily jammed and hurt by interference (to force use of more terrain in groups). Speed always gives nice tactics and range offers even more. My side intention with this is to make gamma bases that are bad or not defended easier to dispose off to make room for others.
This would also make them the ideal bots for scanning on beta. Good detection, fit a masking module and use the speed to find things of value.