I would be pure if I were you and get an escort; that's what I intend to do.
AH but you do make yourself a little more versatile by going in different ships that aren't tactical. Some just want to marriage the tactical officer's capabilities to particular nonescort ships or such :p
I'd say it's viable, but certainly more so for KDF.
If you focus your BO powers towards manouverability and surviveablity, it's suprising how long you can keep a target in your sights for, I switched over to a K'tinga at T3 just because I've always liked that ship, but I found it remarkably good. I was running 3 DHCs, Plasma torps, and 2 turrets. It took a slight drop in damage having less tactical BO powers, but I could hang in a fight far longer than I would have in a raptor, and thus do more damage over a prolonged engagement. I found it especially good in 1v1 duels in Ker'rat. several times I had frequent duels with players of all disciplines and nearly always won.
Cannon rapid fire 1, alpha strike, high yield 1, directed energy modulation 1 and maybe a spot of tractor beam to pin them in place will still do very unpleasant things to what you're pointed at. And if you learn to "slide" your cruiser well, you can make DHC viable on them.
With this setup, the increase in defence is much greater than the decrease in offence. I've no idea how well a tac cruiser would work for me in Starfleet.
the excelsior is a beastly tacticle cruiser, as is the nebula with its universal lt, you can have 2 lt tacs for pairing up 2 doses each of fire at will or beam overload or high yield torps ect. and the excelsior can mount beam overload 3 or high yield 3 or omega 3 all of which make a tac in said cruiser beastly, o ya dont forget fire at will 3! only drawbacks on the fed boats is the lack of dual cannons.
Essentially, cruisers are more for engineer officers, so their consoles will be at commander level. Escorts and such are for tactical officers hence why they have high officer consoles. Each ship type has their strengths for their own type of officer. If there was a ship that had commander level all consoles, everyone would fly that ship. I know I would.
my main uses an assault cruiser noble/sovvie variant, the reason i use it is for complete flexability in combat, with the borg stuff and the best stuff out there it surely helps, in a crunch and given a chance i can tank like crazy and pump in enough dps each time while having enough manouverability added on to make it a bit more versatile getting into optimal firing pattern.
my second uses Defiant retrofit and since the other two variants are butt ugly, that has also got borg gear, its powerful but not as powerful as other escorts i have seen, with them red bolts, apparently more deadly then phaser bolts. i can not tank at all, just hope and get lucky that im not the first target and can use then extra tactical slots to great effect...
in a crunch i would take the cruiser with long term durability and good firepower rather then massive firepower and no durability.
I just switched my Tac from his Escort to an Assault Cruiser, and very happy with the change. I put out good DPS while having much greater survival.
I have been considering the switch for a while, but was put off by the turn rate. Though, I got used to it from flying my Marauder on my KDF guy and now I'm not put off by the turn rate at all on my Fed tac.