I think they are worded differently because they do different things.  The shield/heal can be based on the giver or recipient.

So does this mean Visix the Unboweds shield is based on the combined max hp on all the targets she attacked?

No, it's based on her own max HP, though you have a point that just putting 'her' instead of 'their' would have made it clearer. As Trips said, shields, like heals, can be based on either the giver's HP or the receiver's, but they're not based on the opponents' HP. There's also a few cases where the shield is based on something else, like the damage done with an ability (Miscreated Monster), the giver's defense rating (Valkyrie), etc. 

No, I think you are overthinking it.  It could be their or this, she is the caster & target.  I have never used Visix, so I could be wrong.  Would be an enormous shield in spider for example, so easy enough to find out :)

The OP is correct.

Wording is inconsistent and can be mis-leading. I would also say that some recent new champs have very sloppy wording in some cases.

Take Iron Brago for example:

A1 - Molten Pummeling [DEF]
Attacks 1 enemy. Has a 20% chance of decreasing the duration of all buffs by 1 turn. 

Now, I would like to assume that this skill will decrease the duration of all buffs on the champ you just attacked - but it isn't clear at all. It could mean just that one champ. It could mean the whole enemy team. It could even include friendly champs - it literally does say 'all buffs' - it doesn't indicate whose buffs.

Boo, I agree the wording is often far from perfect.  But in this case it's pretty clear.  If you attack one champ, unless otherwise stated the next part is only that champ and not all enemies.  If it was all enemies, it would state "decrease duration on all enemies".  Again, could be wrong as I haven't build Brago yet :)  

The skills all function in the same way, with the shield being based on the attacking champion's max hp. Additionally, you are a bit off in your interpretation of the skill. If it were written as you suggested, "Attack something and get a shield equal to 10% of their MAX HP", it would be read as being based off the target's max hp rather than the attacker's. However, taking a look at Visix's ability, we see that it is broken into two distinct parts (really 3, but the debuff has no bearing on this) each with their own subject and action. In the first sentence, we see the subject (all enemies) and the action (attack). Following that, the third sentence establishes a different subject (this champion), so the "their" in that sentence is assumed to apply to visix.

You are completely correct that plarium is weird and inconsistant and should standardize their terms.

"Attacks all enemies. Has a 75% chance of placing a 30% [Decrease SPD] debuff for 2 turns. Places a [Shield] buff for 2 turns on this Champion equal to 20% of their MAX HP for 2 turns. " 

As far as I know (English is not my first language), the word "their" is a little bit unusual here, but not wrong. For example my german-english dictionary has: der Existenzgründer [what is singular!] - person [what is singular as well, otherwise persons] setting up their own business.

Agree that the wording is sometimes inconsistent. That being said though, skills in Raid run one way only because of the code, unlike a tabletop game where  different interpretations of how a skill works are bound to come up if the wording is inconsistent (hence the lawyering). 

The only wording issue I know of is the order in which buffs/debuffs are applied (e.g. Block debuff not getting applied first means you're prone to Tormin freeze, etc.) being different from how the skill is described. These inconsistencies have been fixed since. Other than that, I really don't see a significant issue with the varying "their" and "this champion" wording.

I  always  thought  it  was  more  of  a  gender  neutrality  thing,  they  dont  want  to  be  seen  to  be  assuming  gender  perhaps,  their  can  be  singular.  Otherwise  it  could  simply  be  a  performance  issue.  Text  rendering  is  onf  of  the  most  intensive  parts  of  graphics,  anything  they  can  do  to  shorten  the text  string  would  improve  performance,  save  memory.  To  be  fair  i've  never  found  it  unclear.  

To me, this is the one that confuses me. Whose max hp is it referring to? 

i

lol, Madame Serris max hp of course.  this one is easy

What about this one:

Quargan the Crowned

Overgrowth: Heals all allies by 15% of their MAX HP and places a [Shield] buff equal to 15% of their MAX HP on all allies for 2 turns.

I read this that each hero gets healed by 15% of their own MAX HP and then a shield buff is placed on all allies equal to 15% of the combined health of all heroes.

no... not sure why you keep inserting "combined". wishful thinking :)

Of course I knew its hers 🤣. But it says "their"

Now it is becoming more confusing.. "their.." what now? 😂

i

Ok, here is obviously a mistake, but that is more a kind of typo and has nothing to do with the use of "their" in general. It should be "whenever their hp drops below 50%."

What about the first part? Does it heal them by 15% of the casters MAX HP or every allies own MAX HP?

Quargan the Crowned

Overgrowth: Heals all allies by 15% of their MAX HP and places a [Shield] buff equal to 15% of their MAX HP on all allies for 2 turns. 

their own max HP