i kinda do feel like the regen is slower in combat, is there any stat of proof thats true?
It's definitelly true ... it's about 1/3 of out of combat regen and it only works when you don't cast anything. Also buffing your magicka buffs your regen as well, because the reneration is on fixed timers. For example with 100 magicka you regenerate in combat in 90 seconds, with 200 magicka same 90 seconds. 100% mana regen cuts this time in half, 300% mana regen lets you regen whole mana pool in 20 secs in combat.