It's not a storm in a teacup at all. It's not about the money per se, it's about the possible advantage that loaning/donating the £58K gives the loaner/donater.
The PM appears to have an expensive lifestyle, having >= 6 kids, plus expensive divorces, means he is struggling to survive on his PM's salary of £150K.
Lending or donating money to him creates an 'obligation' that will have to paid at some time. This might be a small favour of getting access to the PM to talk them about something, having them lean on a civil servant in a procurement bid, help write an obscure updater to the tax code, perhaps introducing them to somebody in a foreign government. Once you have bent the rules ever so slightly, the next time is easier and the next time easier still. No doubt the PM will bluster as he nornally does, try to switch the topic, but the rules are there for a reason, to stop corruption. Corruption is not normally £100M arms deals to the Saudis (see Private Eye passim), but little things adding up and up and up.
The money means nothing, the debt is everything. I work very closely with govt depts though I am not and never have been a civil servant. I have to be 100% up front about what I can do, what I say and if I go out with good friends who are civil servants, they are very insistent that they MUST pay their own way. There can be no hint of improprietry. I respect that. What the PM is done is appalling, he has opened himself up to suggestions of influence and potentially criminal liability. He knows the rules as he has broken them repeatedly.
I also note that James Clevelly has already started laying the groundwork for the PM not to resign if he has been caught lying. I fully expect other ministers to start supporting this position. So if you're caught taking dodgy loans and you're caught lying to Parliament, does this mean it's still a "storm in a teacup"? please don't say they all do it, so thats OK coz it's not. He's the PM, he's the head of the govt, he signs the ministerial code of conduct and is expected to abide by it though his past history as a serial lier does rather suggest he had his fingers crossed behind his back when he did so.
As an aside it does appear that one can get onto VIP PPE equipment contracts with nothing more than a good word from your local publican to a health minister so Boris might have got a good deal on his loan.
Rob