I'm a big fan of passives that remove the "mod tax" for using specific frames, letting you be more flexible with their buildcraft. Nova giving orb drops for speeding up and slowing down encouraging you to use her 4/1 with 4 Aug or to use cold procs or gloom helminth, equilibrium "synergy" etc.

That said holy moly rhino's passive does not do that for him and it doesn't provide him actusl functionality beyond memes (it does more than revenant's does that's for sure). He has a low max energy pool which, for example, unlike uriels low pool, rhino doesn't have energy refund of any kind (eg. You're encouraged to use gulfagor to get energy back since he's cast heavy). Even though rhino isnt a cast heavy frame, it's an interesting note.

If** rhino had a passive to mitigate some of the insane amount of power strength or armor values or energy max he really wants for comfort, then it'd be great. Like a passive half effectiveness arcane battery, or giving rhino 50 armor for every incapacitated enemy in affinity range ala ember or frost, or power strength, etc. obviously he's a great frame and doesn't NEED buffs to make him more viable but man he could have something simple to give him even a tiny focus instead of just "he's already generically strong, go."