Crapload of armor? More like a metric butt-ton of armor. Along with dual hydraulic flight controls with manual reversion and assorted other features that will allow it maul the enemy, take some punches, survive and return the pilot in a LIC. The political ramifications of a captured pilot are very problematic when dealing with non-state actors.
As for the cannon, to paraphrase from the Army, heavy can go light when required, but seldom can light go heavy. This really gets down to philosophy. I personally believe the single worst thing of all in on the F-35 was the premature shutdown of the F-22 - a no compromise Air Dominance machine. There is a need for a no compromise, spare no expense, latest tech fighter - a Ferrari. There is also a need for a low tech, low expense, heavily armored F-350 duallie. I tend to think that Moore's Law in regards to computing power will render stealth much less relevant over time.
Like the C-130 and the B-52, some designs are simply classic and require only evolutionary updating for their mission.
