Amphibious they may be, but they're very vulnerable without tank support, and they still need decent entry and exit points from the water.
At best they'd be useful to secure a bridgehead (along with infantry) of a few hundred metres or so (covered by tanks on the far shore) while engineers organised a proper crossing for the non-amphibious vehicles.
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If it moves, shoot it, if not push it, if it still doesn't move, use explosives.
Nothing happens in isolation - it's called "the butterfly effect"
Mors ante pudorem
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