1. Ukraine had an antiquated military at the start of the war - old Soviet technology with old Soviet ammunition.
2. Ukraine has used almost all of its ammunition compatible with these weapons, and lost a huge amount of manpower (30000+) including their best troops, and lost 50%+ of its fielded equipment.
3. Prior to the losses and exhaustion detailed in #2, European and NATO backers collected and distributed ammunition and equipment compatible with Ukraine's existing weapon stock.
4. Since exhausting existing equipment and possible sources of Soviet ammunition, Ukraine's backers have switched to supplying Western made weapons. This isn't because they are "better" but because they can be maintained and ammunition will be available for protracted war this is projected to be.
5. Ukraine right now is in a very challenging situation. It has limited equipment of either kind. Their soldiers do not know how to use and maintain the new equipment and don't have much time (due to manpower shortage) to get trained up on completely new equipment and standards.
6. Either way, switching to new weapons platforms is necessary since Russia isn't about to supply Ukraine with more compatible ammunition.
7. Because of the necessity, Ukraine's leadership is "hyping" Western weapons to its people. It's got to tell a story about how victory is around the corner so that morale isn't lost during this transitional period.
8. Western media is picking up on this "hype".
HIMARS aren't going to win the war. This isn't a war of tech superiority. This is a war of grinding attrition. Russia has Ukraine outmanned and outgunned. Western equipment is the only path forward so that Ukraine's force posture doesn't completely atrophy.
The course of the war will be dictated by how either side's logistical, supply, ability to direct and surge force, and the strains on these outlast the other.