Speaking from quite a bit of experience, content can matter at Gmail if it's very obviously malicious/spammy, but not usually otherwise. Metrics matter more than content at gmail.
For other filters/ISPs, content can matter a bit more, but as a general rule for consumer mailbox providers, metrics are the primary thing that affects filter outcomes.
You can even test it yourself without fancy tools by sending emails full of links and mentioning keywords like Viagra et al.