Others champions that rush the same items you said and have more impact are:
= Ult has global presence, more mobility even without TP off CD. Better choice than Taric to go for this high HP build. Plus better lane phase.
= Build in scaling HP synergizing better with Titanic, better lane phase, heavy engage and Shield that scales with HP.
= Skill with HP scaling, better engage and better lane phase.
= Way better lane phase, Shield with HP scaling, more CC and it's easier to land it.
= Great lane phase, build in defense steroids + CC imunity making HP worth a lot more.
So you're telling me I'm suppose to go for a sub-par build, weak lane phase, if I can have more impact going for the same items with other champions?
Taric has to play with his strenghts, he has 2 quick AA that can exploit on-hit items, he doesn't need AS so it's not optimal invest gold in it, thus making the on-hit items we have right now not appealing for him. Going full tank is a bad gamble for him, since full HP stacking Taric is way better as support.
To survive TOP and increase his impact on trades and lane phase he needs a strong on-hit item. Others champions could benefit for those items as well, since right now the only champions that can use on-hit builds are AS oriented.
The game lacks an item that covers AA damage for champions that doesn't synergize with AS and don't have good ratios.
- Doesn't synergize with AS, doesn't have good scaling.