There is no "disproportionate punishment" under GDPR in practice, unless you're doing something egregious, and even then (see Facebook). I'm very familiar with the UK regulator, they publish their enforcement actions [1]. I'm not aware of a single case of a cautionary letter, much less "disproportionate punishment", that they sent over a cookie banner on its own. Are you?
Besides, you correctly hinted at the incentive structure. Your lawyer might advise you to slap a cookie banner just because because they have zero incentive not to, they don't care about your users' experience. You might care though. Personally I consulted multiple external DPOs and lawyers, as well as primary sources, before forming my opinion.
Their position was simple: my team uses 3rd party analytics tools (no ads or anything) so IPs will be passed and cookies will be stored. We don’t control them, we don’t know what kind, if they can be considered personal info or not (GDPR is intentionally vague - classic bad law). So we need to be extra careful since our regulator is not a sane one like the UK’s. Thus: follow the common practice - cookie banner. End of story.
If I were you, I'd consider changing my lawyers. This is explicitly forbidden by GDPR (art 28), you have to know what your contracted data processors are doing, and you have to have processes in place to assure data subjects rights (eg remove their data from your contracted third parties on request). Cookie banners have nothing to do with this, and you're in breach of GDPR cookie banner or not. If your lawyers didn't stop you from breaching art 28 but recommended slapping a cookie banner "to be extra careful", that's a major red flag.
