Here's the problem. Is it possible to be better than Delphi, by only repeating after Delphi?
Not. But compatibility is required if FPC is interested in increase of users audience. But it is necessary to remember that today's Delphi users is not Delphi 7 - guys.
You are confusing Delphi usage with FPC growth. FPC will take the disgruntled users, and those are much more likely not to upgrade.
In XE2 time Embarcadero not had own iOS compiler, but already in XE4 had. FPC was a temporary and limited solution, because modern Delphi features could not be used on iOS and was subject to criticism.
I was told they were originally planning to use their own for XE2, but it was not ready for various reasons, and when it was clear it wouldn't make it for the XE2 release, they reused FPC which they initially meant as a start to develop the libraries in parallel to the compiler to get a quicker time-to-market.
The bit about modern Delphi features is true, but not from users, but from Embarcadero itself. They wanted to have Datasnap mobile clients as soon as possible, and that team too liberally inserted usage of the new features. They probably thought nothing about that because they expected their own compiler to be ready. It was STILL not ready for XE3, so they skipped the mobile offering, leaving users with investments in the cold waiting for XE3.5 (which was sold to them as XE4, of course no discounts...).
So basically it is a story about Embarcadero's failed roadmap planning.
Sure FPC has limitations, but hitting those could easily have been avoided or amended. But they didn't avoid due to their roadmap problems. Amending FPC (even if they had recognized it early enough) was probably politically impossible since they would even have to donate compiler improvements back to a "competitor" because of the GPL(despite that they were eager to use it to bolster XE2 feature lists and make a buck extra of a sale).
Without mobile, XE2 only had 64-bit as appeal.
The rest is just salesfolk trying to cover up, and get you to stump for XE4+ addition to get the mobile offering. (if they were so unhappy with it, they shouldn't have released XE2, they held all the cards and new everything up front, so no excuses)
Don't be a sheep
think! If you really believe Embarcadero's spin of events, get a refund for XE2, because they sold you something THEY say is not up to snuff.
FPC didn't sell you XE2, and didn't make cash on it. Embadero did. The fact that the critique on the XE2 situation came AFTER they sold it to you, and when they had something different to sell to you says enough.