Yep, it indeed looks more like XP classic.

XP has consistent paddings though. In reactos padding on top of the Start button is smaller then on the bottom. Taskbar buttons (for apps) are smaller than start, and do not have padding in between them.

That might be some copyright issues here, you can't make a 1:1 copy of the original Windows shell I guess.

Actually, they already have these tasks in their JIRA, so might get it right eventually.

They seem to be targeting NT 5.2, which is indeed Windows XP, so it makes sense to also target that graphical experience in a sense.

5.2 is windows 2003 / xp-64-bit. XP is 5.1. 64-bit XP was based off of Windows 2003 code base. All are out of support at this point. Doesnt seem like MP or 64-bit is supported per https://reactos.org/wiki/AMD64.