500k/mo account, ROAS down 1.3x to 0.7x - listen to Google RE Broad Match, or no?

Hi r/ppc

I run a business that has a large ad account spending about 500k USD per month and we used to have ROAS in the range of 1.2-1.3, and PMAX performing really well.

Sometime last year PMAX went crazy, serving millions of video views, ROAS started to tank, now at 0.7.

I'm desperately trying to find someone who can figure out what's going wrong, but so far, from my limited knowledge, I see maybe broad match campaigns got created, wasting money (I see a click for "schedule a demo" at $650!) I see opportunities too, restricting geos that have terrible cost per conversion, bid adjustments for weekends that have higher CPA?

I have an ad manager, a Google rep. Google rep basically says spend more, don't add negative keywords, use demand Gen, use AI max, don't touch weekends - all sound like stupid sales tactics to me.

My ad manager is sipping the Google Kool Aid and says adding many negative keywords isn't a good strategy. I have another ad manager on another company I have, he audited the account a bit and said stuff about making the account more efficient by pausing anything with lower than mean ROAS. Google rep and my ad manager are like no bad idea that guy hasn't managed Google ads in a while things have changed drastically since last year, broad match is super intelligent now.

I just need ROAS back to 1! I guess my question is, has broad match gotten better? Do you know anyone who can audit an account of this size thoroughly, taking into acct what was working from last year? Though I want to pay fixed fee, not % lol, and is the Google team (MCS) to be trusted? ​​

Thanks reddit, sorry if this is off-topic for this sub but I'm desperate 😂