From what I have been reading, the greatest concern is still the procurement of weapons systems and munitions from the West.
The process is not as expedient as the media makes it out to be. We read headlines along the lines of "German tanks to Ukraine," yet stories never reflect the nature of difficulties behind it.
Germany, for example, does not have a combat capable force. Finding serviceable Leopard II's was a huge endeavor, let alone the deliberation it took to actually agree to send them.
After serviceable tanks are committed, they still have to be armed with munitions, shipped, delivered, trained on, transported to combat, operate, and serviced.
None of that is easy.
So I agree, Ukraine is under the wing of - in my opinion - American military leadership who are advising Ukraine to operate with combined arms. It is managing logistical timelines that seem to be Ukraine's weakness, not the actual employ of weapons (because donor nations are clearly guiding that).