The phrase "arguably effective" is correct and usable in written English.
It can be used when discussing the effectiveness of something that is open to interpretation or debate.
Example: "The new marketing strategy is arguably effective, as it has led to an increase in customer engagement."
Alternatives: "potentially effective" or "possibly effective."
Banning such organisations was, arguably, effective because the organisations had invested in their titles: they sought to derive legitimacy from their history.
This study proposes a practical life-cycle GHG estimation approach, which is arguably effective to benchmark pavement emissions given project bid tabulation.
The anti-inflammatory relationship was modestly evident for inattentive symptoms in the ADHD group, and arguably effective in countering dysfunction in that higher levels of IL-13 in the controls were related to fewer symptoms of inattention.
Last year's recital by the dream duo of Joyce DiDonato and Antonio Pappano works wonderfully as a double CD - arguably more effective than the concert itself.
There has been less hoopla about Cam Newton's rushing, but he has been arguably as effective on the ground as Tebow.
Muting (which has recently been extended to keywords and conversations) achieves the same on Twitter – and is an arguably more effective weapon against trolls than blocking, which I think can give them a sense of achievement.
"But at the end of the day, I believe he recognizes that there are other, arguably less effective, ways to achieve greater coverage, more choice, better quality and lower cost in our system".
Philippe Coutinho was arguably more effective in the half-hour he was granted, and Balotelli is still looking for his first league goal for Liverpool in spite of a couple of presentable late chances.
The Nelson Mandela 70th Birthday Tribute concert at Wembley Stadium on the 11th of June 1988 was one of the most influential of its kind – arguably more effective than Live Aid for being so tightly focused.
The scorer of the decisive goal in Rio last summer is an effortlessly elegant dribbler, passer and finisher – but one who is arguably more effective playing behind, or dovetailing with a striker such as Robert Lewandowski – as he did to great effect under Jürgen Klopp at Dortmund, and now more rarely under Guardiola at Bayern.
