With every bit of technobabble, the response is always more technobabble. The writers could have written their way around it.
In any other case, I might agree. But the data rod isn't a matter of technobabble. It's futuristic disk. Nothing more complicated about it. Okay, it's a super indestructible write-protected disk, but still. It's not like the writers were going for deus ex machina in this one... For once. Actually I think the writing was very neat in this case.
It's not at all illogical to presume that a shuttle would have limited resources in comparison to a ship, a base, or a dedicated forensic science facility. Indeed, even in-universe, we have instances in which starbases are deemed to have superior capabilities, and sometimes ships with dedicated purposes are called in to continue work our heroes began.
Given that, I don't think it's all that unreasonable to imagine that Garak would want to avoid an unaltered (undamaged) disk arriving at such a facility where the odds of detection would increase.
Then he didn't need Tolar: any programmer would do. And he didn't need Vreenak: any dead Senator would do. If Garak was not committed first to trying to convince the most ardently pro-Dominion member of the Romulan government, and if all he was trying to do was generate outrage, a more impressionable choice would have been better. Indeed, contacting Vreenak posed more risks than other members of the Romulan government.
I don't know much about espionage as a trade -- I'm sure 99.9% of us don't -- but I'd like to think that spies make it a point to do their jobs as thoroughly as possible. If not as a matter of simple professionalism and a desire to be as effective as possible, than at least as a matter of personal safety. Sloppy work tends to create all kinds of problems.
Tolar was necessary to get the best stuff. Would anybody believe that legitimate archive data from the Kremlin would be hand delivered on a simple 3M floppy instead of a nearly-indestructible QR disc? It had to be the best to pass muster. I suppose there are other Tolar's around who could have done the work, but were they available and readily accessible?
And I don't think any dead Senator would do. Vreenak's political position makes him the
perfect candidate. A senator with anti-Dominion leanings returning to Romulus -- dead or alive -- would seem much too convenient.
Imagine the shock over Donald Trump bringing forth documents "proving" that trickle-down economics works? Nobody would bat en eyelash. But if Hillary Clinton was the one to bring that same evidence forward, seemingly intent on endorsing its claims, that would make a lot of people think long and hard about it.
Vreenak's situation is similar. A pro-neutrality person getting killed while trying to bring forth evidence contrary to his position. Now that's
a lot more convincing. It had to be him (or another with similar political leanings).