"Why would you want to be a rogue instead of a college of whispers bard in level 5-10 range?"
It's not a competition that makes one better than the other. Thry bring different types of play to the table. So, I would be likely to play either - tho to be fair whispers is one of my least favorite bards except for the shadow snatcher bit.
Imo if you want DPR combat melee bard, you gotta go MC to get two pally. That way you can smite with those bard levels of spells too. No oaths to complicate things. I think I nicknamed them Shadow Singers in my campaign. Stat spread is an issue tho, but within bounds.
But that aside, I am drawn to rogues by Cunning action (its movement benefits are many), evasion and its various sub-class features from thief, scout, mastermind. Just depends on who I want "this guy* to be.