Spleen Mass on Great Dane- Biopsy?

My almost 10 year old male Great Dane has developed a large mass on his spleen. The vet has performed an ultrasound and has given me a quotation for surgical removal and sending out for biopsy afterwards. He is otherwise very healthy and active for his age, but I have some reservations over jumping right to this surgery with no attempt to collect tissue for a biopsy ahead of time. I asked if aspiration would be possible and they said it would not with no real explanation of why. I inquired about any other possible avenue for a more detailed diagnosis and they are not giving me an answer.

If the mass does turn out to be malignant, my general understanding is that prognosis would not be all that great and then I would have put the dog through a surgery and likely robbed him of some time with a good quality of life. If it’s not malignant, I would be very open to considering the surgery for him.

At this point, it looks like I’m switching vet clinics, because even if they’re correct that this can’t be biopsied I don’t particularly appreciate being tacitly told that I’m not allowed to ask questions about the care my dog receives.

Am I being unreasonable? Is jumping right to a full surgical removal in a case like this with absolutely no idea what they’re removing a normal protocol?