Also if they don't actively defend them, the advantage won't last much; a few wooden boards placed vertically around a small area and a single truck pouring rocks and concrete over it can build a small bridge that would dry in a few days, unless the Ukrainians already have moveable tank capable bridges.
> unless the Ukrainians already have moveable tank capable bridges
I am pretty sure they've had them for a long time, not least because they did multiple river crossings, many successful. Their army is quite capable, and was already quite capable prior to the post-February wave of foreign support. For example in the air defense department, as far as Europe goes they were only second to Russia (though the missiles are starting to run out).
Ukraine was deeply integrated into the USSR and even Russian military industrial complex - shipbuilding (after Moskva sank the remaining best ships in the Black Sea Fleet are made in Ukraine, Mykolaiv I think), engines (both turbojet/turbofan and rocket), whole aircraft manufacturing (Antonov), assembly of armored vehicles ... The lead designer of R-7, the first serious space rocket and the reason why Russians think they won the space race, was a Ukrainian.
