Something I've noticed is that Gemini through gemini.google.com or through the mobile apps is vastly inferior to Gemini through aistudio.google.com. Much worse handling of long contexts amongst other things. Very odd that a product that is free (AI Studio use is free), is much worse than the product I am paying 20 quid a month for.
I find this to be especially true for the newer models like "gemini-2.5-pro-preview-03-25", so if you haven't tried AI Studio yet, I'd give that a go.