When startup funding is scarce, does founding another startup actually help the world?

For context, I’m a student trying to choose a career where they can have maximum impact. One path I’m considering is founding a cleantech startup.

However, I’m worried that even if I found a startup, I might not actually increase the total amount of socially impactful work being done in the world.

Here’s my reasoning: suppose, very crudely, that the total social benefit produced by the cleantech sector scales with the number of cleantech startups that get funded. Also suppose there are more "viable" startups (i.e. startups that could plausibly become profitable if adequately financed) seeking funding than there are funding opportunities. If so, funding my company may simply displace capital from another viable startup. I would change which company gets funded, but not how many get funded, and therefore have little to no counterfactual impact.

I’ve considered a few possible counterarguments:

i) My startup could be more socially valuable than the one it displaces. But in areas like cleantech, many founders are already working on important problems, so I’m not sure I should expect mine to be better on average.

ii) My startup could be uniquely suited to my skills. But uniqueness alone doesn’t imply greater value; the displaced startup may also make a different but similarly valuable contribution.

iii) Exceptional companies can attract additional capital, so capital may cease to be the bottleneck for a sufficiently compelling startup. But founding an exceptional company is extremely rare / difficult, and I’m not sure it makes sense to base a career decision on that outcome.

iv) My underlying assumption may simply be wrong: perhaps there are actually more funding opportunities than “viable” cleantech startups. However, everything I’ve found so far suggests the opposite: there seem to be far more viable projects seeking funding than there are opportunities to fund them.

TL;DR: if I found a company in a sector where many other founders are already doing useful work, why should I expect my entry to increase the total amount of socially valuable work that gets done, rather than mostly reshuffling scarce capital?

I’ve been thinking about this for three weeks and haven’t found a satisfying answer. If anybody has any counterarguments, would really appreciate it...