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It looks like you get a few blooms. Make sure you aren't overfertilizing. Too much nitrogen will bring a lot of foliage but reduced blooms. In fact, most hydrangeas do well without any fertilizer. It looks like they may get a lot of shade. Hydrangeas do best with morning sun and moist soil. They may not be getting much rain under the eaves.

It is the bigleaf hydrangea, and you are right, it blooms on previous summer's bud development. You can see buds on the early stems so you do not want to prune till after it blooms. Your type just has one big show. Unless you have the variety that blooms on old and new wood, they won't rebloom the same summer.

So lack of blooms is not a pruning issue if you are not pruning, so here are some more ideas:

https://www.gardeningknowhow.com/ornamental/shrubs/hydrangea/hydrangea-not-blooming.htm

https://www.gardeningknowhow.com/ornamental/shrubs/hydrangea/do-hydrangeas-rebloom.htm

In a cold zone like yours, a hydrangea that blooms on old wood can fail to bloom if winter injuries kill the stems; in spring, the stems do not leaf out and all new growth consists of new stems that originate from the crown or base. Here in Texas with milder winters, a variation of that occurs: cold in late frost kills the flower buds inside the ends of the stems but the stem is not killed or is not completely killed. Winter protection of the stems ends is then required to protect the stem ends from cold and late frosts. A remontant macrophylla cultivar may be more bloom reliable although a different type of hydrangea may be both more winter hardy and more bloom reliable: hydrangea paniculatas and-or Annabelle-like hydrangeas as both of those usually bloom on new wood, which is normally not affected by winter cold.

It may be from transplant shock and a bit too much water and/or fertilizer. Hold off on fertilizing again for a year; hydrangeas don't need much.

They should be fine. However, if your hydrangeas bloom on last year's growth, you may have cut some blooms off. This year, take note when they bloom and also compare the height, bloom color and shape, and leaves with photos below of the different kinds of hydrangeas. Once you know what you have, you can prune easily, if needed. When in doubt, it's best not to prune at all, except for dead wood like you were doing.

https://hgic.clemson.edu/pruning-hydrangeas/

https://extension.umd.edu/resource/guide-pruning-hydrangeas

Unfortunately, this isn't simple. Mainly, pruning and bloom time will be determined by which of the five types of hydrangea that you have. This will, also, determine if it flowers on new or old wood.

https://www.gardeningknowhow.com/ornamental/shrubs/hydrangea

https://www.gardeningknowhow.com/ornamental/shrubs/hydrangea/when-do-hydrangeas-bloom.htm

https://www.gardeningknowhow.com/ornamental/shrubs/hydrangea/prune-hydrangea-bushes-hydrangea-pruning-instructions.htm

Likely, yes. It does depend on the fungus, though. It looks a lot like watering damage, too. Overwatering will cause wilting like this. It is very important to make sure that the soil is allowed to dry out down to a few inches, thoroughly, between waterings. This will help cut down on infections, as well.

At this time, I would treat with a fungicide. Copper based fungicides are better choices.

https://www.gardeningknowhow.com/garden-how-to/info/using-fungicides-in-garden.htm

https://www.gardeningknowhow.com/ornamental/shrubs/hydrangea