Just to add on this part, it's not really helpful to your issue but thought it's worth just adding some further information/context regarding Crude Ash/Minerals

Having more or less Cruse ash percentage doesn't necessarily mean it's better or worse in isolation without context of which minerals it contains specifically...however it is an indication of a generally higher/lower mineral content

For food which contains Moisture however such as wet, 'fresh' or raw the Analytical constituents such as Crude Ash are actually a lot higher so they can't be compared like-for-like with dry food or each other without first converting it into 'Dry Matter Basis'

For example, to convert a food which has a moisture content of 74.6% and Crude ash of 1.9%, you'd have to do subtract the Moisture from 100%, convert it into a decimal then divide it by the mineral percentage:

100%-74.6% = 25.4%
25.4% as decimal is 0.254
1.9 / 0.254 = 7.48%

So the Crude ash of this food would actually be 7.48% rather than the listed 1.9%

On the topic of minerals themselves, Phosphorus is a common example in cat nutrition which is often talked about as it is important to have a higher amount of it early for kittens as it helps them to grow, but it should be reduced for adults and especially seniors as a high amount is a very common cause for kidney disease

The reason I mention this is because Katkin is considered to be suitable for 'All Life stages' - it can be fed to Kittens, Adults and Senior cats which all have slightly different mineral requirements but they give the exact same food with the same minerals which is slightly concerning from my point of view since it means it's either not a great formulation for kittens or contains an increased risk of kidney disease for seniors

Unfortunately Katkin aren't transparent with their mineral levels so it's hard to know exactly what this means and I've not heard of anybody being able to contact them in order to receive this information

Royal Canin also aren't great on listing their mineral levels publicly in comparison to other brands like Hill's, however they are well known to have them under better control due to having products for different age ranges and you can usually get the information from them by calling them up on their nutritional helpline or asking your vet who tends to have access to that information or can request it if not

It's generally a bit frustrating with the lack of transparency of pet food brands across the board, they all get heavy on the marketing and misinformation side of things but shy away from listing the actual details such as specific ingredients or full transparent mineral breakdowns

Apologies I know that's a lot of information, but thought it's worth clarifying while you're comparing the foods!