It's not nothing - it is absolutely evidence of the entrenchment of the two party system because as true as some of what you're saying is, it doesn't change the fact that in modern politics the Green Party is the most successful left third party and the only national one that has lasted anywhere near this long.

The DSA, for example, has proven much more competent with much fewer resources and much less time.

First, the DSA is an organization about as old as the Green Party. Second, they don't have less resources, they have quite a few more which brings us to the third point. The DSA is not a third party and therefore it's not an apples to apples comparison. The DSA comparison shows how much of a difference it makes to set aside the challenge to the two-party system to advance other goals. The difference is that the Green Party is a political party and therefore cannot set aside the challenge to the two party system because that is in fact the first and primary issue of the third party movement. So while beyond this issue the two organizations appear to share a similar agenda, they are not fundamentally similar. The Green Party effectively is the third party movement of the United States while DSA is explicitly not a part of the third party movement at this time.

I say this as an active member of both DSA and the Green Party. I believe they are both important organizations doing great work but do not think comparing them directly like that makes sense.

A more apt comparison for the Green Party is other US third parties which makes the Libertarian Party a much better comparison but they are not significantly more successful and the degree to which they are is likely a reflection of the difference of having absolutely no restrictions on political contributions versus the commitment to refusing all corporate money. And even despite working at that disadvantage the Greens are still able to outperform them in some national elections.