Not all dilutions are created equal. Eduardo Saverin was aggressively diluted out of Facebook so that Mark Zuckerberg could take control. Multiplying the number of shares in the company and redistributing them like that is a totally, utterly, and completely different thing to taking on £20m of investment for 25% of the company. You are comparing apples with oranges.
You’re making a new investment, at a different price. And you are choosing to maintain an arbitrary proportion of shares in the company as a total.
You are forgetting that the pie is getting bigger. A smaller piece of a bigger pie, which will grow bigger via the investment. Your money will grow. Nothing is unfair. It’s just a logical fallacy that you need to keep your 0.0033% of the company until IPO.
Actually, the opposite is true. Subsequent rounds will (hopefully!) be for increasing amounts of cash. Say the next round was for £100m [Edit: I meant £200m). In this round ~10% is allocated to crowd funding - which only amounts to a couple of million. In that future round 10% would be 20 million. 10x the number of people could invest. However, I doubt that Monzo would go that high; the market for crowdfunding has its limits… And it makes a pretty bad press story to not fill a round like that. If I were them, I would make sure that was not a risk at all.
If you still don’t believe that investing in the next round is a completely independent event, then take a look at the calculations in this spreadsheet. It shows that buying shares to compensate against dilution in Round 2 and Round 3 leads to exactly the same profit as the sum of the two separate cases where you (case 1) don’t purchase against dilution and (case 2) you buy new shares in the same proportions as an anti-dilution purchase in Round 2 and Round 3. They are independent events! Provably! (43080 + 31440 = 74520).
