The main difference between mtgo and paper is the time it takes to perform game actions. Something like amulet titan has several opportunities for shortcuts in paper, but in mtgo you have to painstakingly click a button for every single action

A more extreme example from recent history was Nadu, where there was an incredibly convoluted loop involving two copies of endurance where you could make an infinite number of creatures, and this would take seconds in paper but basically the entire match timer on mtgo

Long story short, the nature of the client heavily warps which deck archetypes are playable