Does Kratom tea make Kratom stronger??

Well in theory the raw leaf will have the most alkaloids, even a thorough tea won't absorb everything. Also not all the alkaloids may be equally water soluble, so you could get stronger effects from specific alkaloids absorbing easier as tea, but you will always lose some alkaloids.

Alkaloids do absorb easier in tea, so you will get quicker effects that might feel stronger but get processed more quickly.