I find that a 16:1 or 17:1 ratio delivers the coffee flavor more reliably. But, most morning I forgo this and do a 20:1 or more just so I have more to drink over time. The higher ratios, being weaker, seem to be more forgiving in terms of bitterness (makes sense cause the flavor is more watered down).
1:12.5 seems really high, imo. I've always been told 1:16-1:18 and get good results. I agree with the other comment in that a new grinder is what you should be considering
You reversed your coffee and water in the 12.5:1 portion.
Measuring is important for repeatability but getting a good grinder should be your highest priority. A Timemore C2 will be a huge improvement over the blade grinder. You should be able to find one for around $60 most places.
Mugen: 1:18 usually, V60: 1:16ish. (Light and medium roasts)
Ratio will depend on preference, equipment, and what coffee you're brewing, as well as the recipe. In my case I use a bit longer ratio on the Mugen compared to the V60 because it has less bypass (less water gets around the coffee by going through the filter too soon). Generally speaking folks use shorter ratios for darker roasts and longer ratios for lighter roasts.
It gets a little more complicated with iced coffee, because what you're doing with iced coffee is actually brewing a very short ratio and then diluting it, which gives you a concentration that is similar to what you would normally get, but with lower extraction. (Not necessarily a bad thing!)
Like most basic entry-level coffee nerds, I do whatever James Hoffman tells me to, so I use ~15g of coffee to 250g of water (which is equivalent to the 1 to 16.7 ratio suggested in your link).
I think it's still worth playing around with ratios regardless of grinder, it definitely could still make a substantial difference in your cup. However, switching to a decent burr grinder would be a massive difference both in quality of results, but (perhaps more importantly) reproducibility. Blade grinders make it harder to achieve the same grind size every time, and even within a single dose the ground consistency won't be great.
A caveat I'd like to add: blades are known to produce a lot of fines, which causes higher extraction. So maybe the lower-than-typical ratio you've ended up on "compensates" a bit for the high extraction. At the end of the day though, remember: who cares what some website/James Hoffman/random Fediverse users have to say? Do you like the coffee you make?
When I switched to pour-over, I didn't want to futz with figuring out the proper ratio, so I bought a grinder that produces pre-measured amounts, and a pitcher with measurement lines. So I go with the "2 cups" measurement on both.
I personally do a 20g:300ml for hot coffee or 20g: ~320ml for iced coffee (only approximate because of the ice cubes)
So that ends up being a 15ml per 1g
Also i think you mixed up coffee and water in your post, isn't it 12.5g water to 1g coffee.
Does it even matter to adjust the ratio precisely if I don't have a precision grinder and am using a Krups blade grinder? I am trying to get things as precise as possible.
Consistency allows for reproducible results but there's diminishing returns at a certain point. My grinder is the type that has a big hopper and runs for χ amount of seconds and I don't notice a difference even though it can be up to 1g up or down.