Not all chargers are able to charge at the same rate. The combination of phone and charger matter. I have some really fast chargers, but they work better for some phones than for others. 

I wouldn’t worry about going from 98 to 100% in general anyways. How long does it take to charge overall atm? How long was your phone call? Phones typically use up a lot of battery for the first couple days before they sort of “settle in.” If it doesn’t get better in a few days, you can see what’s using up your battery life in your battery usage settings. It is possible that you have a bad pixel and you have 30 days to exchange/return in case it doesn’t get better.

Phone will charge much quicker from 0% to 80% than it would from 80% to 100%.

In many cases, the chargers and cables have different currents and voltage. You might want to look into a charger that is best compatible with your Google Pixel 6, as it is clear it is not working as well with your Samsung charger. 

In the worst case scenario, you can return your device within the 30-day period if you bought it online. If you wish to proceed, make sure you send them an email at koodo.webstore@koodomobile.com to initiate the return process. https://www.koodomobile.com/en/help/returning-or-exchanging-your-koodo-phone

Comparing charger specs, Google’s 30 watt charger has three additional voltage steps, (15V, 20V and 21V) which should allow for faster charging.

Google 30 Watt Charger

Samsung 25 Watt Charger