There are many types of hydrangea, some are smaller, some larger. Some get pruned to the base every year, others merely get dead-headed (dead flowers are cut off), to encourage flowering the next year.
These are hereditary differences.
As far as flower color, pink or blue, that depends on the ph environment of the soil in which the bush grows.
I wish I could figure out which type of hydrangea I have.
One of the two in my garden is pictured above.
The other has never bloomed. I am reluctant to cut all the branches to the base, for fear none of the branches would return the next spring.
The two specimen that I have were acquired at different times from very different places, they both get a lot of sun exposure and their local ground has been enriched.
Various hydrangea could be like relatives, they are in the same family, but even siblings are different from each other.