Are you sure you mean the Peroneal Tendon / muscles? The ones on the OUTSIDE of your calf and ankle? I ask because, if your foot collapsed, that would cause (it seems to me) to have those things SHORTEN, not get pulled tighter. Conversely, a collapsing arch will cause the muscles on the inside of your calf and ankkle - Posterior Tibialis muscle and tendon - to get longer.
I think wearing a brace is not a good idea at all. It just encourages the joint to become weaker. (You're telling your brain it can use the brace for support - so those muscles go on vacation. They don't have to work so hard. Alternatively, if there is no brace, then the system knows it must take full responsibility, and as a result get stronger.
Now that doesn't mean you just take the brace off. You have to rehab and make the ankle strong. I *strongly strongly strongly* recommend you go to a good PT. And I think a good rule of thumb when determining if your PT is good or not is whether they assess your hip function. If you go in with ankle pain and they ONLY focus on the ankle and calf then I would fire that PT and go look for another one. You want someone that is checking your hips in addition to the rest of your leg/calf/ankle/foot. Weak and poorly functioning hips can cause all sorts of issues down the chain. I had chronic heel pain and my PT found a problem with my hips and the heel pain went away. She did no "PT" on the heel.
Lastly, I would stay away from orthotics for your "collapsed arch". Orthotics, IMHO, are way over-prescribed. Many many problems that conventional wisdom says need to be fixed with artificial support can instead by resolved if you put effort into proper function, strength, balance, etc.
Good luck.
Jim