In the first case, say I have 100 different type of errors of which some are these kind of conflict errors. So wouldn’t it be sensible to have a feature to dismiss/suppress such known errors and pass the ERC check ? How is one supposed to deal with multiple types of such errors reported by the ERC and get around the problem otherwise ?
Errors such as supply pins being connected to GND, or pins not connected are indeed important warnings and errors which should be corrected depending on the type of pins.
The correct way to go here is to fix the symbol. There will always be some mistakes in the official library. So you will from time to time need to correct something by having a copy in your personal lib.
In the end ERC and DRC are very different tools.
DRC is a strong warning that your PCB has errors that are likely to make it not manufacturable.
Every DRC error needs to be carefully thought about.
ERC is a hint to the designer that there may be problems in the design, it cannot do the electronic design for you. The example of multiple output pins connected together is a typical weakness of the tool