I am well aware of that fact and would not seriously propose you to implement such a change as stated. I was simply pointing out the core issue and why it exists in the first place and to put into perspective how your proposed change relates to the problem which it tries to solve.
Either way, it won't seriously impact me as I don't actively use this method for energy transport (precisely b/c I think its counter-intuitive to transport energy with anything other then CARRY).
When you buy a brand new car from a dealer, you instantly lose 30% of its market price, and it makes perfect sense.
Except that is one of the canonical examples of why car dealerships are infuriating to deal with, precisely b/c it doesn't make sense.
If you want to restrict the player's ability to convert between raw energy and creeps, even if its a design choice I personally don't agree with, thats still fine.
The issue is, this doesn't really fix the problem that you claim you want to solve. If you want to transfer a large amount of energy via creeps, then using HEAL parts is still going to be a better option then using CARRY parts (unless you want to use boosts, which was still the case even before this change).
While I agree that its kind of silly that you should use anything other then CARRY parts to transport energy/resources, this change is just a pretty crude fix to treat the problem, rather then actually cure it.
The core issue at hand here, is the fact that CARRY doesn't hold enough energy relative to the cost of the other creep parts. In essence, the energy content of a single HEAL part is equal to the carry capacity of 5 CARRY parts. I don't think nerfing recycle is the proper way to fix this imbalance, but rather adjusting either part costs or carry capacity is the more proper fix.
Additionally, applying a flat 30% tax on creep recycling feels like a sudden departure from the way other other game mechanics are balanced (e.g. creep renewing cost/tick time), which is that of a near zero-sum game. With this change, the instant I spawn a creep (regardless of purpose), I lose 30% of the energy cost of that creep instantly, which I don't think makes any sense.
The idea that you get less energy back for 'used' creep parts is already implemented as is, i.e. older creeps return (proportionally) less energy based on TTL. So I don't really buy that as justification for adding this recycle tax.
I think being able to fluidly convert between raw energy and creep parts is a really nice design choice, that shouldn't be abandoned simply b/c players are using creep parts in ways they weren't originally intended. It's also not like there aren't other cost factors the come into play when turning energy into creep parts (i.e. spawn time/pressure, CPU costs, etc.), so there are still interesting optimization choices to be made on the part of the player.
just my 2c
Interesting ideas, I do think that there should be a lot more emphasis on protecting the controller during a siege. Since one of the biggest advantages a defender has is the freedom to choose where to place all of his or her structures. This means the defender can cluster all of their buildings together in a extremely compact defensible position. The player, however, does not get to chose were the controller in a room is placed. This can force a very significant additional constraint on the defender when planning his/her base layout, but only if attacking the controller results in a serious penalty to the defender.
Instead of (or maybe in addition to) the current effects, attackController could build up some counter, which if it reaches a certain threshold will temporarily reduce a rooms RCL by 1 for some number of ticks. This would mean an RCL8 room would lose control of 3 towers, 1 spawn, 4 labs, and all the other buildings that become available at RCL8 making defending significantly harder. The main idea here would be that this temporary downgrade would be achievable on a much shorter timescale while still requiring a strong presence in the room by the attacker. Furthermore, it would potentially promote extended conflict around both the controller and the defender's core base.
Perhaps this idea is redundant with respect to the way attacking the controller is currently implemented, but I feel like decoupling the 'upgrading' aspect of the controller from the 'attacking' aspect would give a lot more flexibility to properly balance this mechanic.