It's worth keeping in mind that there were 22 US Army divisions in the Pacific (not inclusive units in transit from the ETO at the end of the conflict, not including independent Battalions or Regiments) at the end vs the grand total 6 USMC divisions (same disclaimer as with Army in regards to independent regiments/battalions). Some of these units were late arriving (5th and 6th Marine Divisions only made Iwo Jima and Okinawa respectively, 98th ID basically missed the war, making it into theater in time for the war to end, while 93rd ID saw action fairly late but did not experience much combat compared to it's peers) but generally speaking much of the fighting was indeed shouldered by the Army by sheer numbers alone.
It's hard to encapsulate the performance of an entire branch across the Pacific because that leads to speaking in generalities, and there's a wide gap across time and experience (or even in similar geography, US Army, Philippines 1941 was a totally different beast to US Army, Philippines 1944-45)
The US Army's performance compares well to the Marines in regards to battlefield victories and effects. The key things that enabled the US success over the Japanese arguably had less to do with different branches, and more to do with things the American military writ large brought to the fight (superior logistics, overwhelming firepower, increasing air/sea control etc).
However,
There is a joke/commentary I pulled from "Touched with Fire: The Land War in the South Pacific" by Eric Bergerud. To paraphrase, the Australians were seen as the best jungle fighters, followed by the Japanese and USMC. No one was sure how well the US Army would fair in a jungle fight given it's tendency to knock it all down with artillery prior to attacking.
This could be taken as illustrative. The US Army did favor a more methodical approach to battle. This antagonized the Marines to no end and would boil over into some of the worst inter-service "combat" (in terms of spilled ink and raised voices) at Saipan.
However inter-service sniping aside, again, the US Army did accomplish its missions, and did shoulder a significant amount of the fighting, including some of the only true urban combat in the Pacific War (battle of Manilla), and several paratrooper attacks, and daring raids behind enemy lines (the raids at Los Banos and Cabanatuan are some really interesting reading at least!). The Army also tended to inflict the same sort of disproportionate losses on the Japanese that the Marines did (just to keep with the Battle of Manila, US Army forces lost 1,010 KIA, 5,565 WIA to the 16,665 counted Japanese military losses, additional example, with elements of 2nd Marine Division, the US Army lost 250 KIA at the Battle of Gifu, in exchange for 2500-3000 IJA KIA).
The Marines being a feared unit in the Pacific would entirely be an opinion judgement vs something you can really quantify. The Japanese military and civilian response to either US Army or USMC units tended to be fairly uniform.
For further reading/sources:
"Touched with Fire: The Land War in the South Pacific" by Eric Bergerud. Highly recommended as it spends significant time examining the respective military forces involved in the Pacific conflict.
"Ghost Mountain Boys" by James Campbell. Discusses early US Army offensive in the Pacific. Grim reading.
"Eagle Against the Sun: The American War With Japan" by Ronald Spector. Great strategic overview of the Pacific.
"Implacable Foes" Waldo Heinrichs. The last 18 months of combat in the Pacific, inclusive both US Army and USMC operations.
"Guadalcanal" by Richard B. Frank. The Marines carried the opening land battles of the land component, but the Army ultimately finished it. Worth a read anyway.