You're absolutely correct that he could have aimed towards that ending.

You guys should have watched Babylon 5 instead. The last ep was 20 years later. Sheridan died. Delenn lived quietly in retirement. Londo and G'Kar died. Vir became emperor. Garibaldi married and lived happily ever after. The station was deemed redundant and blown up. The End. Probably the difference was that JMS planned B5 to run five years, then end. Martin probably intended his thing to be an income generator indefinitely. Without a planned ending, he can't start the arcs that produce a satisfying ending.

Unusually for American broadcast television at the time of its airing, Babylon 5 was conceived as a "novel for television" with a pre-planned five-year story arc, each episode envisioned as a "chapter".[3] Whereas contemporaneous television shows tended to maintain the overall status quo, confining conflicts to individual episodes, Babylon 5 featured story arcs which spanned multiple episodes and even seasons, effecting permanent changes to the series universe.

Wikipedia: Babylon 5 - Wikipedia

A couple guys who run a "reaction" channel on YT started watching B5 a few weeks ago. They are still in the first season. One of them commented recently that comments on their reactions keep saying "you haven't seen anything, yet", because we know what is coming. They haven't met Marcus, or Cartagia, yet. They haven't seen the assassination of President Santiago, that really kicks off the Earth arc.

Steve