Wy is benadryl (diphenhydramine) more effective for hives than allegra?

Not always the case: yes benadryl (diphenhydramine) is an effective medicine and stood the test of time, but different patients respond differently to different medications

Not true.: The second generation antihistamines ( cetirizine, fexofenadine, loratadine) are just as effective as the first generation ( diphenhydramine, hydroxyzine). The effect you see may be difference in dosing?