I agree that that can be a cause for damage and that is only going to be a problem when the computer is not adequately earthed itself. ...
Surge protectors on consumer units are a good idea I agree. We have one since we had PV panels installed. Here in the UK it is mandatory for all new consumer unit installations and replacements but that still leaves 90% of houses with old units that don't have a surge protector.
In the UK, surges are so rare that if any protector was effective, then nobody has surge damage. Since appliances contain robust protection, then damage in the UK is rare. But UK has surge damage because most have no effective protection from that rare type of surge that overwhelms existing appliance protection. Protectors adjacent to appliances will somehow stop a surge? Of course not.
Earthing an appliance makes that appliance an easier and destructive path to earth. Apparently a few concepts are not understood. Some call that third prong on a power point an 'earth ground'. It is not. It is only a safety ground. Earth ground is another and different ground.
Inside your computer is a digital ground and analog ground. That is different from the safety ground, which is different from the earth ground, which is different from a floating ground found inside some electronics. Those grounds may be interconnected. And are electrically different.
For example, many only assume a wire from a power point ground to switchboard is 1 ohm. It better not be that high resistance. Meanwhile, resistance is irrelevant. Critically important here is impedance. That wire that should be more like 0.1 ohm resistance can also be 120 ohms impedance during a surge. Assume a surge is tiny - 100 amps. 100 amps times 120 ohms means the voltage (end to end) on that wire is something less than 12,000 volts. Where is the earthing? Does not exist because that wire is too long, has splices, has numerous sharp bends, and is not separated from other non-grounding wires.
The term is 'less than 3 feet'? It was critically important. Numbers in that above paragraph demonstrate one reason why. And demonstrate why a power board or appliance only has a safety ground connection; not an effective earth ground connection.
You also assumed earth ground conductivity that is irrelevant because it is high. A surge current flows through miles of earth (to earthborne charges) no matter what you do. The question is how that current gets to earth. From the cloud, through 3 kilometers of sky, then through kilometers of earth to earthborne charges. Ben Franklin demonstrated how to make that connection without structure damage. A lightning rod does not do protection. (Many foolishly argue pointed verse blunt). It is simply a connecting device to what does the protection - the earth ground electrode.
Lightning striking any utility wire (overhead or underground) far down the street is a surge incoming to all household appliances. Which one makes a destructive connection to earth? That one is damaged. Same 'Ben Franklin' concept applies. A protector does not do protection. It is simply a connecting device to what does the protection - an earth ground electrode.
In both cases, protection of a structure or appliance is not defined by what everyone sees - a lightning rod or protector. In every case, protection is defined by the most important component in every protection 'system': earth ground. Both lightning rod and protector are only as effective as the most important item in any protection system: earth ground.
Telcos all over the world do not attach protectors adjacent to their electronics. That would only make surge damage easier. In every telco (ie BT) exchange, always installed is the single point earth ground (better earthing) and 'whole house' protectors. Every wire that enters that building is earthed by a protector. To make protection more effective, telcos increase separation between protector and electronics by up to 50 meters. Separation (and that 'less than 3 meter' connection to earth) is critical for protection.
How often is a destructive surge? For homes, typically once every seven years. A number that is much larger in the UK. However telcos connect their £multi-million switching computer to all other buildings in town. That means about 100 surges with each storm. How often is your town without phone service for four days while BT replaces that computer? Never. Because they use proven protection. Protectors make a connection from every incoming wire as short as possible (ie 'less than 3 meters') to single point earth ground. Protectors are separated from electronics by up to 50 meters.
Foolish is to think anything (fuse, protector, open switch) will block a surge. It was not stopped by kilometers of a world's best insulator - air. Why would millimeters inside a fuse, RCD, etc stop a surge? It doesn't. Nothing stops a surge. As in nothing. Furthermore a fuse, RCD, etc take milliseconds to trip. A surge is done in microseconds. Maybe 300 consecutive surges could pass through an RCD before it even thought about tripping. Anything that would stop a surge is best called a scam.
Either a surge connects to earth harmlessly outside. Or it connects to earth destructively via appliances (or a structure - even wood is an electrical conductor). Only the consumer makes that choice. Damage means a surge was all but invited to go hunting for earth inside and destructively via appliances. Protection means that current has a much lower impedance (ie 'less than 3 meter') connection to earth on a path that remains outside the building. And so again, protection is defined not by a protector. Protection is defined by the quality of and connections to single point earth ground.
It should be obvious that nothing (not an RCD, switch, fuse, filter) stops or blocks a surge. Do not earth an appliance. That only makes that appliance the best and destructive path to earth. Earth a surge (maybe 20,000 amps) before it enters the building.
You had damage? That was the path an electric current took from cloud to distant earthborne charges. Damage because that current had (simultaneously) both an incoming and an outgoing path to earth. At the same time a surge is incoming to a power board protector, the same current is outgoing into attached appliances. Nothing stops or blocks that current. High voltage (and therefore destructive energy) only exists when something foolishly tries to stop that current.
A protector is only as effective as the quality of and connection to single point earth ground. Earth the surge; not an appliance.