I get the impression that its a science ship and has limited armaments. It was likely never meant to head outside of Federation space nor get into this type of combat and their armament wouldn't have even been impressive 20 years ago.
Even the Nova class (for planetary surveys) was seemingly better armed than the Titan-A and survived in the DQ for a long time... and in Endgame, we saw the Nova class got a pretty sizeable upgrade by 2404 (at least in the alternate timeline).
It seems to me that SF took a u-turn at some point.
Why would you want to be sent on a mission even inside UFP space when you know space is unpredictable and on more than one occasion we had very bad things happeneing near the outskirts of Federation space, and inside it.
Plus, this is the 25th century... you can't seriously tell me that SF would allow a vesself to continue functioning in the field for 20 years without getting any upgrades in the meantime.
VOY got a badly needed refit/repair in Season 7 (and that was only due to lack of accessibility to a decent port in the meantime - even Torres said that it was put off for too long).
For ships operating inside or near UFP space, they would be getting regular refits every 3 or 4 years. The Galaxy class was refitted after BoBw concluded (which was at the start of Season 4).
So, every 3 years or so, ships would get refits/upgrades most likely. Some might take longer to get their upgrades if they are on longer haul missions.
It seems someone just didn't bother with the Titan-A in that case? Even then, I doubt this oversight would have lasted THAT long. Somoene on the crew would have noticed that they are posted on an outdated tin-can (and don't get me wrong, even if the ship design isn't 'new' as such, that doesn't mean all of its internal tech wouldn't be modern - essentially making it modern through that)