This looked odd.....

That does seem a bit too extreme, but way to many capital ships is his first problem. There is absolutely no reason to build 9 Kols unless the enemy has an unholy amount of strike craft, and even then I don't think you'd need more than three even in the worse case.

The AI fleet composition would also be a very good counter to your friend if it was larger. Progens/Iconas combo is probably the most effective defensive tactic in the game, and its especially effective on the TEC who can't pierce shields. In addition the main use for the Radiance is as a capital ship killer, which is your friends entire fleet. Was his whole fleet destroyed or did he retreat before then?

9... Kols.... wow 

Their combined GRG might actually scratch a shield.

My guess would be that the Advent was stacking nearly maxed-out mitigation bonuses.  Advent can hit upwards of 90% mitigation on capital ships when all things are maxed out.  It's entirely possible that his Iconus/Progenitor combo was restoring shields faster than your friend's relatively low-firepower fleet could dish out damage.

As the others have indicated, Kols are a bit of a joke.  TEC, particularly late game, is dependent on fielding overwhelming firepower, and capital ships have relatively low firepower, and the Kol is one of the worst offenders.  For the same price as 9 level 4 Kols, you could build about 170 Javelis LRM.  That would kill most capital ships in less than 10 seconds, and even with maxed out Advent bonuses we're looking at a longevity of less than 30 seconds for that formation.

 I am guessing the levels on the Advent ships were higher than level 4. 

Just punched a few (rough) numbers for this scenario.  Your friend's fleet has a dps somewhere in the range of 700, but due to the heavy reliance on Kols this would be spread across multiple enemy units.  With six units, that works out to an average of 110 DPS to each enemy.  After damage reduction, though, you're probably looking more at the range of 15-30 damage per second to each individual.  A Progenitor can restore 60 shields per second to every single unit surround it.  Basically the AI had a defensive combo going powerful enough to render it invulnerable to your relatively weak weapons.

May I ask a question? What in your opinion is the best cap ship in firepower? 

Any Carrier Cap.

In general, capital ships should not be used as your primary firepower.  Early-game the Marza and Sova (for TEC) can have a commanding presence as combat units, but this role tapers off in the late-game and they become obscure support units in any major battle.  If you can get them to high levels they can be absolutely amazing, but capital ships share experience, so if you have too many capital ships it's virtually impossible to level them all up.  So in practice, the general consensus is that TEC should have 3-6 capital ships in the late game, no more.

The best way to deploy firepower is through frigates and cruisers.  As TEC, that means the Javelis LRM, the Kodiak Heavy Cruiser, and the Percheron Carrier equipped with bombers.  Fighters, flak frigates, and hoshikos make excellent units to round out your fleet.  TEC really has no business with large swarms of capital ships; I've experimented heavily with large numbers of caps, and it really only works well for Advent, and for TEC you virtually never want more than 6 caps.

A Marza using Missile Barrage, if you can pull it off.  Otherwise, what Darvin said.....

Goafan in answer to your question, he got away with 1 sova and the marza.