Lump in cats stomach

So about a week and a bit ago, we noticed a lump in our cat of 7 years stomach area (under the skin) and took her to the vet.

This vet essentially said to give it 2 weeks, if it doesn't go down then it's most likely a tumour but to prepare for the worst as the lump is just below the size of a golf ball.

My gf being a massive worrier, had a panic attack and took her for an emergency vet appointment 5 days later as the lump hadn't changed in size and she was losing more and more weight.

This vet essentially said "In my opinion...I'm 99.9% sure that this is cancerous and is going to kill her. I would put her to sleep to save her the pain". I not feeling comfortable having panic driven from work simply said we'd return the next day so we could spend our last evening together as a "family". They said they'd be closed the next day but would book us in with another vets.

So we then go to this vets (yesterday) who has all the notes and such from the previous vets. State that he'll take a look but we should be prepared for the worst after he checks. After he comes out he simply asks "Has she been eating?" to which we reply "Yes, none of her usual eating, weeing or pooing habits have changed. She's just now spending all of her time in the coolest part of the house". He then responds with "ok well in my opinion and I've gone through the notes...and it's more of 50/50...there is clearly something there. At the minimum I advise you get some blood work done, then we can tell if it's something that we should take a further look at or if it is something that is inevitably going to kill her regardless of what we do"

We've now opted for this option and have had her blood work done (test come back tomorrow). We're not getting our hopes up and nor would we put what we consider a family member through pain but I'm just amazed by the varied advice we've had from these vets. Additionally, some form of factual evidence warrants the need to put an animal down...not someone's advice. I get it's professional advice but still.

Has anyone else ever experienced this? Just seems so bizarre that a first response is the unprofessional equivalent of "just put it down".

Edit: Just to make sure you all know. The vet has assured is that our cat isn't in any pain whatsoever, even when touching the lump. She's just drained energy wise and has a temperature.