I tested DNA Siphon on both live and test on a Stalker with the same power slotting and Offensive Adaptation on, and the drop in effectiveness is pretty stark.
With my slotting (admittedly with no +Heal slotting), I get the following:
Test - +150.59 HP on the main target, +45.18 on subsequent targets = 421.67 HP (standardizing to 7 targets).
Live - +150.59 HP on all targets hit = 1054.13 HP (7 targets hit).
Setting aside the effect adaptive recharge has on procs (which is honestly whatever, losing AoE damage isn't ideal but oh well), that's an approximately 60% decrease in the heal for a set that has no other heal.
Obviously /Bio's survivability design ethos is more about Absorbs and +Regen, and those values should absolutely be factored in when trying to analyze and balance the performance of the set, but on an AT like Stalkers who see less relative value from Absorbs and +Regen because of lower Max HP caps this change marks a significant decrease to the overall survivability of the set. Especially when coupled with the additional -Defense that now comes with using Offensive Adaptation.
Maybe reverting all of the changes to the healing component of the power is an unrealistic ask, but keeping 60% of the effectiveness of the heal rather than only 30% on subsequent targets would be a welcome change.