Yes, all of these statements are correct. Massive mana upkeep, and prep time (prep being defined as utilizing his class spells, not additional preps for damage redux, etc).
However, highlights and aliases simplify the prep and upkeep. Gearing for mana also assists with the vast amount required to prepare and maintain. When you're duo'd, since you can still locate targets with the 'where' command, it's not really that big of a deal if your opponent leaves. Much like a stalking assassin, you go back to square one if you have to. Consider that it takes far longer for an assassin to start stalking all over again than it takes for a transmuter to reprep to engage an opponent, and that a transmuter who sneaks (race inherent or through an item) they can usually get a lot closer with a lot less exposure risk than an assassin.
A transmuter can initiate a fight with lagging attacks, weaken you with spells in the duration, and toss out a lot of damage, so drawing the fight out against a transmuter is rarely an option. Yes, updates to most fighter classes provide the ability to cause bleeding, but by the time you've switched weapons and utlized this tactic, you're dead. Sure, maybe once in a while someone is prepped and ready for it, and puts up a fight. But more often than not, as you see from the logs being posted, people are dead before they even have time to fart in fear or surprise.
The class needs to be toned down. These drawbacks are minimal for a patient player.