Answer: Plants can take quite a long time to become established. While the second tree rose is growing slower than the other, I don't think planting on the site of a former pine tree is the reason. Unless, of course, the stump and roots are crowding the roots of the new rose! Roses don't like competition from other plants for moisture and nutrients.
I'd continue to give both roses plenty of TLC, and wait to see whether the puny one catches up to the other during the course of the summer. If it doesn't, you can dig and replant it during the dormant season.
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