I must for the most part, agree. I've heard the same from a few other GSPs. Much of it still feels dated, and customers don't seem to like looking at console windows for simple custom scripts we have in place. It has its own set of quirks (for our installation anyway - scripts don't automatically execute on triggers half of the time, etc). Then again, it's generally a very reliable package of software that we can depend on, which is key.
We had a team approach us recently asking for our thoughts on a direct TCAdmin alternative, and whether or not we'd consider a switch if they offered a means to migrate the database side of things. I've also tried out the alternative which I believe you're mentioning. Our live TCAdmin installation is nearly as fast - speed has never been an issue since our most recent infrastructure upgrade.