It does seem a bit ridiculous especially as there will be two six nations championships and two Rugby Championships played before the RWC and a couple of Autumn test matches too.
I guess they think the top 3 southern hemisphere nations of New Zealand , South Africa and Australia will not alter much in the rankings same as the top three Northern hemisphere nations of France , Ireland and probably England or Scotland will be the same.
you partly answer the issue yourself.
you state two 6 nations and 2RC's to go - (actually wrong - see below)
if you accept for a start that the last rounds are too near the World Cup as the rankings are also used to seed junior nations and determine who may automatically qualify and who has to face playoffs. That leave just on around left
rankings/seedings for the Fiji, Georgia and USA of this world are determined differently as they don't have the tournaments like the 6 nations and to a large extent the Autumn internationals when many like Fiji play the bigger nations and that helps determine the rankings. After this Autumn there is only one more round of Autumn internationals next year and that is far too close to the world cup for play off etc to be organised globally (remember qualifiers have to play din specified windows of international rugby to allow for player release from clubs) so this November realistically becomes the cut off round of games
the rankings are always a bit misleading anyway - which one of the 2 big tournaments do you use as a cut off date? England could win all five of their 6 nations matches in '26 and move well up the world rankings whilst NZ and SA are totally inactive and don't even touch a rugby ball - that isn't really painting a true picture. Equally in the Rugby championship SA may play NZ twice at home, win them both and jump ahead of NZ courtesy of home advantage so that doesn't paint a fair picture and the info below could distort the rankings even more ....
if you were to check the latest facts the 2026 Rugby championship is NOT being played at all so that distorts rankings further. New Zealand are playing 4 tests away in South Africa in August and September so getting real ranking stats from that will be awkward. At the same time Australia and Argentina do not play each other 4 times to balance matters and Argentina don't play NZ or SA
I totally agree that the system is flawed and illogical but to find abetter cut off a date nearer the world cup is very difficult to establish as time is so restricted for player release and dates available to pay all qualifiers. If they used the end of the 6 nations as a cut off date England feasibly could win another r7 games before then and jump further up the rankings than might be the case after a 2026 rugby championship , if it existed
the Lions tour also throws a curve balls as all the summer the home nations tour with reduce strength teams that may have led to unfair results and an adverse effect on their rankings
so many factors to consider, perhaps someone could come up with a better option.on here .....
In contrast qualification for the soccer world cup 2026 started officially in September 2023! Nobody is complaining about that