They have about the same physical bulk in terms of base defense stat: however, Florges's is slightly higher, 68 to Sylveon's 65.
If you apply the same ev spread to Sylveon, it's stats compared to Florges are lower in everything relevant to a defensive set except HP, which admittedly allows Sylveon to beat Florges in size of Wishes, which on this set is half of the purpose of the HP stat in itself. However, the difference in total is only 34 points, 17 Wish-passed HP points gained in using Sylveon over Florges. With Florges and this spread, it's stats are higher than Sylveon's by 7 def points, not all that serious, but more importantly in sp. def... Florges beats Sylveon by 48 points with the same ev spread. Adding the fact that Florges outspeeds Sylveon naturally, with equal investment, by 30 points, makes Florges the better defensive fairy pokemon with this set. The ev's are intended to allow Florges to utilize it's already huge special bulk, while still investing enough in physical bulk so that it can adequately take less powerful hits from that side without problems.
Sylveon has more offensive presence while using defensive sets, but I don't really care, I would rather have the extra speed. The loss in HP passed in wishes wasn't entirely a problem, but my team sufficed well enough on wishes of 176 or so that Florges passed.
Also, I'll admit that a factor in using Florges outside of my genuine opinion that it is defensively superior was that at that point Sylveon was the first popular Fairy type that a lot of people ran to try out the type, and that popularity grew into most Sylveon sets acting as purely special wall/clerics on teams. Physical counters were the most effective because it's defense was far lower, and often left without ev investment. Many just thought of Florges as a fundamentally inferior Sylveon and would expect to OHKO with non SE hits that it would eat up. This made Florges even better in my eyes.