While I see what you mean, this generally doesn't change many of the champions its suppose to hit.
Most champions that have shields still want to interact with the enemy to ensure they don't get away or that they stay away from their ally/adc.
will throw out Q and W, which will put her in combat if it hits.
throws most of her kit at the enemy once she uses Mantra E so she can get mantra again and be useful so she's usually always in combat.
Q's the enemy to slow them, W will CC them and ult will also CC them, so it puts her in combat.
Throws out Q which will put him in combat if it hits, and he pokes with W passive auto, additionally his E does do damage after awhile so it will eventually put him in combat if it hits. I'm pretty sure Daisy hitting someone puts him in combat, though I'm not exactly sure.
Q poke and passive which will put her in combat, which she usually wants to use to benefit her team with its aura.
wants to constantly hit Q so she can sustain her self enough to heal and E is very important to her impact without her heal and it puts her in combat.
Q will put her in combat, and her W which she sometimes doesn't have a lot of control of herself (it relies on ally and enemy positioning, more so than hers a lot of the time) if it bounces to an enemy will put her in combat, if an ally hits an enemy with her E I'm pretty sure it puts her in combat too (not sure about that one).
Will Q to stun and his heal isn't that great and is mostly used out of combat, which means if someone uses it even though he's not in combat it would put him in combat even though he isn't.
Uses his E mostly for mobility but he's very short ranged for an echanter mage so he's usually in combat anyways.
Mostly the same instance (except mobility obviously) as Rakan, short ranged and his stun puts him in combat.
A lot of these champions are already in combat when they shield, and will cast spells that hit enemies even when they are themselves are on the run. I don't think this will really change much, but having it in wouldn't really hurt anyone except maybe Bard since he puts shrines down for his allies to use around the map.
Most of the champions in the game aren't going to be spamming their shield/heal without interacting with the enemy, they're not going to sit back and just do that, they will often also be using their other abilities while autoing.
Also apologies for grammar errors, I'm tired and sick atm lol.