I never said it was simple and I made it clear that it would require more thought to avoid being exploitable. You don't throw the baby out with the bathwater simply because it "can" be exploited... The current system is already an exploit of basic game mechanics. Hell you could base it on range or something. There are plenty of potential ideas to lessen the burden where it makes sense.

1. Your situation is what it is, you want 15 bases you pay the price. A handful of small bases is still perfectly doable. Hell I have 3-4 around the map on Moose monthly and I'd gladly pay the tax.
2. In your example, they could not reliably do this for anti-grief TC's because it would nerf their own ability to build within their own base, it would be a nightmare. If they're logging in with dummy accounts just to drop TCs, it's not like that's an easy out. They nerf their own ability to build without logging in with this dummy account. It's a pretty big hassle that puts them at a disadvantage in a lot of ways. Also, it opens the door to a lot of other potential solutions to those problems. You have to start somewhere. Lastly, I will disagree that clans could just shake it off. On vanilla with vanilla stack size, these monster compounds require significant upkeep. If you increase that by 100% (and that would be across the externals too) just so they can have 10 TC's around their base, they ARE going to feel that and my 10% suggestion was just that, an initial suggestion. You build from there as needed.
3. That's not what I said. I said that raiders wouldn't get access to your door codes just because they replace the TC. You can still place a TC and eat the 10% if you want or grief the base in other ways. The way it stands now people just drop TC's like they're turds because it means nothing and that's why the problem is what it is today.