Regarding the oakleaf...do you have deer or any other animals in the area that could be browsing on it? They did that to mine after planting them 4 years ago. Since then, I have protected the oakleafs with barriers and they seem to have finally gone gangbusters this year, and look so much better/healthier. If not deer, it could just be a transplant shock/problem. Try leaving it where it's at and maybe give it some mushroom compost and water regularly this season. I have heard that Oakleafs take their time getting going, and I can attest to that. The last 4 years mine looked scraggly and sad. Give it some more time. I am 99% sure that I have also fed mine Holly Tone, for acid loving plants. That may help too.

No, the frost could have damaged them still. The damage can occur when the leaves are still in a leaf bud. Tiny things, almost invisible and hard to distinguish from a flower bud. After leaf out time, the damaged area would have looked normal (just an example), may have dried out, or may have been infected by something (fungus, etc). You can cut the petiole of the worst offenders if they bother you but it is not something that would kill the plant or something that can be undone. Iron deficiency shows up as light green leaves or yellow leaves whose leaf veins remain dark green. Your pictures do not show that symptom. Make sure that the leaves are not getting watered via overhead watering to prevent fungal issues. Also, make sure the plant only gets morning sun (afternoon/evening shade). I could not tell if there was mulch but it will help keep the soil evenly moist and will reduce the number of waterings.

If last year's stems fail to leaf out and all growth in Spring comes from new stems, this hydrangea may require winter protection to bloom reliably. It probably develops invisible flower buds in late Summer or early Fall at the ends of the stems. These buds should then open in Spring but, if it gets too cold and the stems get killed, you get no blooms. Winter protection in the Fall would help with that. I put chicken wire around some of my hydrangeas and fill the inside with mulch. A few weeks after my average date of last frost, I remove the winter protection and use the mulch elsewhere. If you are pruning it at some point, consider that the invisible flower buds develop in late Summer or early Fall but they then open in the Spring. Thus it is best to prune no later than the end of June so no flower buds are pruned off. If you have any old stems in Spring that do not leaf out by the end of May, prune these all the way down by the end of May.

When a plant is root bound,the water runs down the sides of the container and does not reach the middle. Take your plant and put it in a large pot of water. If it bubbles, then the water is replacing the air in the rootball. When the bubbling stops take out of water and let drain. Now for the hard part! Cut the roots that are circling the pot and the pull the roots out of the tangled up. You will not kill the plant. Untangle just like you would to untangle a little girl's long hair. Next, trim off the really long roots so the fit into a new pot. The next size is usually selected. Shake the old soil off the roots and place the plant in the new pot. Add soil to the bottom of the pot and holding the plant, add soil to almost fill it up. Use any bagged soil - organic not necessary - tap the sides gently to settle the soil and water and let all the excess water drain out the bottom of the pot. Next step, cut off ALL the old blossoms! I would cut the leaves in half but they will eventually fall off when the new growth pushes them out. Do NOT ADD FERTILIZER OR ANY CHEMICALS! Put the pot and trimmed plant out in the garden or porch and leave your plant alone for a few days. It will recover and you have learned skills that can be applied to almost all house and garden plants.