Resources like Zagat were helpful but could only get you so far.
In pre internet days if you were flying to far away places like India or Vietnam where your local airline didn't offer service, you would have no resources available for finding or arranging flights, hotels, or other transport. That's where a travel agent was helpful.
These types of travel agents still exist but they’re generally specialty travel, adventure travel, etc. companies that handle a combination of group trips with guides and private trips with or without guides. Besides the big global ones there are many that concentrate regionally and/or in a particular type of activity.
When travel agents were local shops, like a local boutique clothing shop, it would seem they had a lot to lose and not that much to gain by working against their customers interests.
In short I wouldn't say "never".
Travel agents were never on the side of the consumer. If you asked travel agents who they perceived they were working for, they'd tell you it's the airlines. This is not just my opinion; in travel industry magazines, articles, etc., this definitely was their stance. They'd choose flights for you that were most profitable for themselves and/or the airlines (and those two factors coincide nicely). Even pre-web, I almost always found a better prices by phoning the airlines directly if I wanted to spend the time.