Hi there, OP!
Trinity is no more oversubscribed for Economics than most other colleges. We recommend that applicants don't choose their college on the basis of how likely they think they are to get in based on statistics, not least because statistics don't give you the full picture. For example, College A might have 60 very well-qualified applicants for 6 or 7 offers, whereas College B might also have 60 applicants for the same number of offers, but they're not as strong. A strong applicant therefore has more chance to get an offer at College B in the year we're talking about, but the statistics don't reflect this.
It's also worth noting that about 20% of applicants who are made offers at Cambridge are given offers by a college that wasn't the one they applied to because they were put in the Winter Pool. Strong applicants from any college can be pooled and may well be made an offer elsewhere, so the numbers of applications vs offers at any one college isn't the whole story.
I'd also say to think carefully about how you understand someone telling you that you have a 'strong' or 'good' chance of an offer. This isn't directed at you specifically, but at anyone applying. It's worth remembering that what the person telling you that you have a 'strong' or 'good' chance of an offer thinks that means and what you think it means could be very different. If you understand a 'good' chance to mean 'you've made yourself as competitive as you can and at this stage of the process, but you're still competing against over 1,000 other applicants for around 150 places', then you might have a different understanding to someone who takes it as 'you are more likely than not to get an offer'.
I hope this is helpful!