Your position is well thought-out, but I find this hard to believe. Simply put, amassing between 100,000 to 200,000 troops on the border of Ukraine, deploying warships to the Black Sea, and positioning troops north of Kiev--is an obvious, obvious indicator that Russia was prepared to use military force. Even when it looked as though the Russians were escalating to de-escalate, we had US and UK intelligence agencies outright coming out and claiming that Russia was amassing for an invasion. They were even laying out Russia's possible (and probable) invasion strategy.
No, I don't think the UKA failed to mobilize because Putin played his hand well. The UKA failed to mobilize because Zelensky is a fucking idiot. He failed to mobilize the UKA in response to the Russian threat, I expect because he didn't want to help feed into any possible Russian false-flag operation that would act as Putin's golden ticket to invade Ukraine with the blessing of the Russians and some Ukrainians. He perhaps thought that if he could avoid flinching, that Putin wouldn't attack, because he would lack the excuse.
Now, I can't speak to military strategy to any strong degree, but I think this is what happened. I think that US and UK intelligence actually did learn what Putin's invasion plan was. With Russia taking chunks away from Ukraine and slowly escalating from there, until it took Kiev. When the West exposed those plans, I think Putin and his generals were put in a tight spot. They couldn't go through with those invasion plans now--but they couldn't turn back either. And the West was not giving into their demands.
So I think what Putin and his generals did was switch gears to a new plan, which involved an all-out assault on Ukraine. Zelensky, who had been convinced through allied intelligence what Putin's invasion plan would be if it came down to a war, did not see the telling signs and not wanting to provoke Russia, did not mobilize the UKA. It looks to me that Putin and his generals then launched an all out attack, hoping to crush and demoralize the Ukrainian forces before they could even mobilize.
I think the result has been a mix. The UKA was not properly mobilized and Russia was able to inflict heavy damage that they might not of otherwise been able to. That said, while the UKA was never properly mobilized in time and suffered heavy losses because of it, I think the UKA did not break as Moscow had hoped. And instead, Kiev is now using social media and some blatant propaganda to counter mobilize widespread resistance to Russian invasion. It's difficult to tell what sort of effect that is having--because Kiev is going to do all that it can to make such a move successful and the West is going to feed into it.
I think what is happening is that the ad-hoc plan that Moscow had used has run its course. It had a mixture of success and failure, so now Moscow is switching to a new plan. I think the danger is that the Russians were not prepared for this sort of attack logistically, which is why everything seems so sloppy right now. The shift in strategy is coming/already in the works, so what happens now is probably going to be even more dangerous.
I think the real key here is just how strong the identity of Ukrainian nationality really is. It's a difficult game. The Russians need to break the UKA's will to fight, without killing too many civilians, otherwise it will just redouble Ukrain's willingness to fight. At the same time, Zelensky's propaganda, while somewhat unexpected, has been weak and even ham-fisted at times. Zelensky only needs to overextend himself or suffer a large defeat for his warrior-king image to evaporate back into the ether from which it came.