Holy Shield is somewhat of a fringe talent (and one I've never personally been a huge fan of the design of, even if it's undeniably useful) in the sense that it doesn't actively change how you play per se, but its simple existence forces players to not only consider what type of damage they're taking, but how said damage is patterned. Its design could absolutely have been better and it's far too close to a truly passive talent for my liking, but it also does create a player skill distinction in the sense that it requires more than a basic understanding of the game to consistently identify when Holy Shield is an appropriate choice and when it will amount to jack shit.
TL;DR: Holy Shield has plenty of reasonable justification for existing, but it's not a talent anyone should be sad to see go if they chose to replace it.