schem minus the tier three super weapons (artillery primarily as the nukes have a powerful counter) and experimental units beyond tier three it is very easy to turtle.
T2 arty base, T2 TMLs, T2 combined force approaches
going around back
bombing runs
Mercies, if you're advent (the horror, the horror)
yes, T3 is the easiest ones to crack defenses with, but to say that the superweapons are there because the ability to turtle is a broken part of gameplay? I think you should get your head checked.
I mean, I should still list the T3 possibilitites
bombers, siege bots, T3 arty bases, nukes dont count whatsoever, but coastal bombardment
the super weapons (artillery is not a superweapon) are there because at the end of the game it can easily default to a war of battle attrition, they're meant as a cleansweap at the end of a game.
supcom's turtling is more than under control, unless you outproduce your enemy and shield and place T2 arties zealously on Isis, but thats an extreme case.
Tier 2 weapons especially with shielding are effective against most attacks... even if you launch a big attack they can have multiple layers of shielding and task engineers to the shields to extend their life.
Furthermore, with a good airforce it's hard to get anything really nasty close to a base. Battleships, all ground based experimentals, and all but the eier 2 AA ships are very vulnerable to tier 3 bombers... and tier 3 fighters knock most air units out of the sky very quickly.
as a general rule if you can do any damage as the attacker in supplement to hitting your enemies forces you've gained a massive upper hand
taking down turtles is as easy as choosing the right side to hit with a few dozen tanks or a bomber run, of course its not the instant-win that the T4s are, but its definately garunteed to crack a turtle
as for shielding and T2 weapons: use mobile artillery, or a close by T2 firing base. if you're having difficulty cracking a turtle in supcom its because you arent going about it correctly, or they've developed some miracle system that to date I've never heard of.
I feel it is a great solution because those who want to use them can and those who don't can simply turn them off
the dev's have a problem with this, because they claim then they would have to balance both games
hopefully they can do that anyhow.