It's not about quantity but quality.
One backlink on Forbes for instance is more worth than 200 backlinks on plain and general article sites or PBN's. In this niche relevance is key. You can read our article about the relevance here and you may read our article about the special YMYL and E-E-A-T-protocols of Google for Gambling websites.
The problem with those links you mention is that they come mostly from blackhatters. In most cases they generate toxic links for you and therefore risk Google Penalties or get you lost in the Google sandbox in the case of a new site. Both for a very long time.
In our strategy we avoid toxic links to keep your link profile healthy and avoid penalties. Toxic links some agencies use come from spammy sites, irrelevant guest posts or bad link schemes.
In order to keep your site safe, we check at first whether there are toxic links. If so, we send Google a disavow request to ignore those bad ones from its index. This helps prevent penalties and secures our link building efforts we have planned for you.