I have learned since I got the new mixer that I didn't know what dough strength was prior to seeing it for myself. I'm sure it's possible to do by hand or even with a Kitchenaid, but the stuff that comes out of the spiral mixer is just plain strong. Smooth as silk as well. I go by dough temperature and not time, but I probably mix most types for about 10-15 minutes.
If your loaves are flattening out they just aren't strong enough. If you are using bread flour then that shouldn't be the issue. It just needs more mixing. If you are doing the no knead recipe, I'm not sure where the dough develops it's strength (time?). I know pro bakers that have made a living with it (Jim Lahey) so it's obviously possible.
Mine are proofed in 10 inch oval bannetons from central milling. Flipped out on either parchment paper or the peel. Slashed, sprayed with water, and launched to the stone. You can be fairly rough with them and they stay firm and sturdy.
You can learn alot about dough in this channels videos. This guy kind of yammers on many times but is a wealth of info for new bakers. They started in a garage a few years ago knowing nothing about baking and now have just recently moved to a brick and mortar after being forced out of their garage. If you go back in their videos it is actually a pretty awesome story. Most of them are long form like an hour or so unlike most fast and furious channels and they are very informative. At the 1:15 mark or so of this video you can see him flipping out the bread. It looks very similar to mine in the way he flips it. The bannetons are the same as well. I don't use liners though.
https://youtu.be/0S2vlh9_FhcI will post the recipe in a little bit.