The phrase "arguably would have" is correct and usable in written English.
It can be used when discussing a hypothetical situation or outcome that is open to debate or interpretation.
Example: "If the project had received more funding, it arguably would have succeeded beyond our expectations."
Alternatives: "potentially could have" or "possibly might have".
But Encarta arguably would have failed even without that competition.
And yet, if he had put bipartisanship ahead of legislative victories, his Presidency arguably would have failed to get any legislation passed.
These results were significant, and arguably would have been even stronger had the authors been able to distinguish between executives who knowingly misled and those who did so unwittingly.
Such a move arguably would have averted the debilitating down-to-the-wire negotiations this summer, which Mr. Clinton says left the United States looking "weak and confused" to the outside world.
Although other leading camera firms also came under extreme pressure at that time, had Kodak's management moved more quickly, it arguably would have bought itself valuable time to explore other options.
The replacement arguably would have helped a considerably larger number of people.
"Arguably this would have been exceeded if the country had not been 'closed due to snow' for two weeks in December," the SOLT said.
This problem could of course be alleviated somewhat if instead of merely appealing to modal structures as such, one could appeal to modal structures that arguably Aristotle would have thought are part of the very fabric of the world.
But arguably, it would have the strongest impact on revitalizing and humanizing American politics.
Arguably, it would have been more difficult to land instruments on the moon prior to the detonation, which the 1959 paper recommended.
Many stakeholders incorrectly viewed the centrally held NHS dental budget as 'non-cash limited' and arguably, few would have referred to NHS dental services as particularly 'resource constrained'.
