Well, you probably will be able to test stuff on Test Center. But people have complaints about it too:
It's too much work to make appropriate gear and whatever you end up with may not match what you'd actually use on your normal production shard. (Apparently imbuing on TC isn't really the answer to that complaint either because it seems that you don't get the whole range of imbuing ingredients in your bank box by using a command. Or if it's possible, no one remembers the command from the beta.)
There's too much lag because morons deliberately litter the ground with certain items.
It's a pain in the neck dealing with bank storage. And the commands you use to get stuff on Test Center only work once per character. There are no commodity deed boxes because there are no vet rewards. And see the next point about housing. If you ain't got a house and all you have is your bank box, enjoy the process of managing all those resources stuffed in your bank box that you MIGHT need to imbue or craft yourself something you need.
If the shard is a brand new special one or is the old one that was wiped of all characters and houses, unless the devs put up a special gate or program a special rule, your character has to be at least 15 days old to place a house. And even if they go with an existing test shard where perhaps you already have old characters, good luck finding a place to put a house to store stuff.
You have no way to know which factions are active and who is in them or how many points it will take to get the rank you need to wear certain artifacts.
The cap on real skills is stuck at 700 no matter how old your account or character is.
There's no possible way to get vet reward items.
The new robes and artifacts aren't available via a command and some of them obviously aren't available at all even if you were willing to go out and kill stuff over and over and over ad nauseum to get them.
You have to wait for your pets to bond unless the engineers put up a pet bonding gate, something they rarely do. Do you normally use a dread mare? Sorry, they don't exist on Test Center. You like having a trained war horse, you say? Not likely to happen on a Test Center. Even if you can't buy one on Origin, at least you can import one, right? (If you act now, that is.)
You have nothing built up in any virtues you might use. (Yes, the engineers can put up "instant virtue" gates (why does that sound so bad??) on a test center but again, they rarely do.)
Origin may not be the perfect alternative. But I think it comes a lot closer to what you'll find on your home shards than a test center does. Plus the characters you make there are permanent. For some people, that might make them take testing more seriously than using a temporary character that might be wiped out without so much as a moment's notice. After having your character and the time you took to craft and assemble gear and mark runes and join a faction with your mates wiped out at least once, a lot of people just give up on testing. I saw it happen last summer in the SA beta and that didn't include testing anything as complicated as the faction system. Every time there was a wipe, the number of people logging in to test stuff dwindled even further because they got tired of recreating everything. You think people will go through all that on a test center for factions? Nope, it will not happen or happen for long enough to do anything more than just superficial testing.
Also, if the new stuff they put in involves wiping out or adjusting points, ranks, faction membership, etc. on existing characters, how the heck do you test that on a test center where every character is new???
Plus if you actually build a new character or two on Origin, you can later move it to another shard. Can't do that with a test center character.
And who knows....maybe if enough people do this, eventually they might all get their characters built up enough to have some truly epic battles on Origin. The kind that are the basis for movies and require planning that people aren't likely to do when everything they need for the movie could be wiped out in literally seconds and with no advance warning.
So, speaking of faction movies, anyone still have the link for that good one? I think I need to watch it again.