To be fair, you are now grouping in zones designed for level 66+ on a character that is still 65. It's not like you are still fighting in LDoNs and now you can't mez mobs you could before. Similar to if you had stopped playing during Luclin expansion and came back after PoP to find you could not mez anything in BoT. Five expansions have come out while you were away, and to expect to be able to waltz into MPG and be able to mez at 65 seems like wishful thinking.
The pattern you see for the future goes into the past too, Enchanters have ALWAYS suffered from the gaps for mez at various levels. This is not something new. Level 59 mez up to 61, level 61 mez up to 62, level 63 mez up to 65, level 64 mez up to 68.
The answer (which I hate, but is still true) is to level yourself and get the new spells. Yes, you may be stuck grinding in level appropriate zones instead of fighting only red cons, but such is the price of the bottom-feeding enchanter in a group setting.
You are probably right that no other class has such restrictions on one of their class-defining abilities. Enchanters have been nerfed pretty hard over the years, and I think it's partly a testament to how god-like a well-played enchanter can be. If they change something then somewhere a crackerjack enchanter is gonna find a way to use it to do something that makes others jealous, and then the nerf bat comes out. Hence, the limitations on enchanter mez. They don't want enchanters soloing or trivializing content that should be cutting edge for them or their group.