Or am I worrying about this unnecessarily?
You are. Provide a lot of amps. Each device will take just as much as it needs. So err on the side of more watts - it will even help your batteries charge faster.
The only thing that can be diminished with fast charging is the number of battery cycles (the battery lifetime) so set a low charging engage (only charge if <= 50%) and a high ceiling (stop charge if >90%) in your bios: this will increase your battery life.
Source: all my devices use USB-C. They all share the same AC adapter with power delivery, and a Lenovo Dock also USB-C with PD.
No USB-C charging = I don't buy.
The batteries of my 7 years old previous laptop, which was used mostly stationarily and mostly kept at 75-80% state of charge, are still at above 90% capacity. I don't fully trust the >90% reported, but the batteries are quite obviously still good.
The reason was airplane seats. They have a breaker that flips at 75W.
I wouldn't get fast charging with the 60W adapter, but I wouldn't run out of juice on a 14-hour flight.
The devices that are being powered are the ones controlling the charging, the charging brick will derate itself if devices demand more than it can handle. It might hurt the brick, it will get hot or perhaps noisy if it’s a cheaper one.
It’s like openning every single faucet at your house, as long as the pressure and flow at the source are ok, the faucets will output the same as in any other case, otherwise each faucet will “slow down”.
Basic charging works on the principle of deciding a charging voltage (which is either 5v or negotiate to be higher via Power Delivery) plus as many amps as the charger can provided.
As a receiving device the only thing you really care about it voltage. If it’s to high, then stuff gets fried, two low and stuff just doesn’t turn on.
The amps are determined by how much the receiving device can consume. And of course decreases as the device charges (if you’ve got a full battery, then you don’t need more power). If the receiving device pulls to many amps, then the voltage will start to drop, this then causes the receiving device to reduce its power consumption.
Ultimately power electronics are extremely robust today, you would have to try very hard to fry modern electronics. This is a result of how modern electronics converts power, which naturally makes them very robust to fluctuating inputs. (I’m simplifying a lot, want to learn more then look up DC-DC converters, and see how they’re implemented in silicon)
In short, just don’t worry.