Battle of Kapetreon Hard Mode (need help)

The first thing you need to buy or get is some wardrums, they were really helpful in this level. To complete this level capture the city south of you first. Send your deployed general and another gen to take the northern city. Have the remainder of your troops wait to take the remaining city in the south. Once you start attacking the north, it triggers an event, which lures the enemy gen north to fight your deployed gen. Use your troops in the south to take the city. While, use your deployed gen to kill the target gen and the city. I would suggest deploying Cnut, as he tanks a lot of damage and he is very good at killing enemy target gens.

It sucks that not only your enemies' troops will be lvl 10, 11 and 12 while yours of the same tier can't go over 6 or 5 (due to Campaign restriction)

But its not only your troops the ones with level deficit. Your allies' troops will also suffer it. And worst of all, on this mission you do take 4 attacks to the face before actually starting to play yourself, leaving you with lower hp starting troops for your gens.

I did this mission recently, but I do have Richard, so not F2P. I don't know your generals, but what I did was ignore the top and middle path to the east, that should be the last city to take. Southern city is the first priority, then go for the one in the west, and then from there go North, but do leave someone at that city behind you as soon after packs of 3 troops will spawn below the city and aim to retake it. The two troops at range of the city should attack it twice each with some siege eq, the two of the right should retreat and defend with the fortress, which will lure the foes into you giving you the advantage. You'll need to even use wardrums on turn 1 to hit hard on the city, which you should take on turn 2 (between another 4 attacks and the fortress troop capturing it).

Your ally won't help much, but expectations of allies in hard missions are very low, and even with such low expectations, they still disappoint.

If you still find it too hard, you can wait until the next patch comes, which will allow you to raise your troops' level further, making hard campaign easier.