No he's not right. The reason why the all in one had to be downloaded once is due to the change from regular kro/sakray to renewal. Official items changed/ IDs changed, maps were added etc etc. The info that's stored in the data.grf/sdata.grf got merged and changed. Aside from those files we have 'custom' files. Like our own sprited headgears, a way to connect to our server and the other custom things we have. Those are stored in the server files not in the sdata.grf. In other words the all-in-one gave you a newer sdata.grf with the renewal files included to it (which is the same as having the renewal clients downloaded). All our server-side files are updated with our patcher, this does not make any changes to your sdata.grf only to our server grf files.
The requirement to download the all in one was to support the change to renewal (new maps and such). And we still very much advice to download the game through our all in one installer. However, the small patcher/installer is sufficient with the newest renewal clients downloaded. However I will not guarantee that you will be completely error-less if you install the game through different ways than the suggested way.