I have no idea who Tal Celest is, but if she was an ensign then, yes, she would have equal standing as an ensign on the Enterprise. Maybe an enterprise ensign would have had a bit more prestige, maybe theyd actually be better at the job. However, they are both of the same rank and would be expected to perform the same duties competantly.
Tal Celest was an Ensign that barely made it thru the Academy and couldn't perform her duties on Voyager because to spite her ranking, she couldn't understand the jobs she was given. Therefore he skill level wasn't near ANYONE of her rank no matter what starship she was on. You can't expect someone that graduates with straight A's to have the same skill level as someone that graduates with straight C's.regardless of rank. That's why the reward of good grades and excellent service is to serve on the Enterprise.
I dont think Sisko built the Defiant, and remember that episode where O'Brien was off doing something else and the whole station was suffering. O'Brien was always on a tight schedule and you could see his was pretty vital. Torres never seemed like the centre of engineering in that way, often characters just took over from her.
Sisko says he helped build it in "The Search".
Don't you find it odd O'Brian has an entire Engineering staff that can't do their job while he's gone? You don't find it far fetched that one man can fix an entire station as large as DS9 all by himself? It's not only unrealistic, it's nearly impossible.
Yes, Torres works smart so she doesn't have to work hard.
Part of being a good boss is training your staff to carry on work while you're away or delegating work to others to get it done faster. Regardless of who ever does the job, B'Elanna still gets credit because she head of the dept. and trained her staff well.