The phrase "arguably as big" is correct and usable in written English.
It can be used when discussing the size or significance of something in a way that suggests there is room for debate or differing opinions.
Example: "The new smartphone is arguably as big as the previous model in terms of market impact."
Alternatives: "possibly as significant" or "potentially as large".
These attitudes create a challenge for the Republican Party that is arguably as big as its better known struggles for the votes of Latinos.
Now, though China carries political risks arguably as big as in South-East Asia, investors have had a dramatic change of opinion about the respective potential rewards.
On the Web, which even rivals have long considered a strength of the Obama political apparatus, criticizing Mr. Romney has become arguably as big a focus as defining the president.
UFC has also won acclaim for its determination to give its female stars equal billing with their male counterparts: Ronda Rousey, for example, is arguably as big a draw as fellow fighter Conor McGregor.
And Marion Jones was arguably as big a track star in America as one can get.
Religion is by its very nature big, arguably almost as big as humanity itself.
"They are arguably not as big as they once were – and they were once absolutely huge: Idol is a cultural phenomenon in the US – but they're still big.
Local commerce is a huge chunk of the economy, and whoever brings those businesses online successfully could arguably be tapping into a market as big or bigger than online search advertising.
The challenge of managing and adapting the MTF as big companies grow increasingly global is arguably a greater one than making any particular ruling, however tricky.
The peculiar fact about the current crisis is that even as big papers have become less profitable they've arguably become more popular.
Large pieces of work such as big books are set and cast on a Monotype machine, arguably one of the most complex mechanical devices ever made.
