Divine Sorceress who gain +1 attack but loose 1 life

Since it blocks 1 attack which would probably kill it anyway, 1 extra magic power is much stronger, so I think it's an acceptable trade-off specially when cards like Archmage Darius and Delwyn Dragonscale exist. It's going to hit for at least 6 magic attack in total before dying - and that's assuming the opponent's magic reflect monsters aren't dead yet. Because if they are, then she might even a free pass combat pass thanks to Defender of Truth + Armorsmith.

Other example: The Flesh Golem loose three times (Level 3 to 4, Level 6 to 7 and Level 8 to 9) one life.

That's because of how heal works. Heal is based on how much total HP a monster has. Flesh golem won't heal more by being at 10 hp because the rare earth summoner already gives it +1 hp anyway, so it'll heal for the same amount even if it's sitting at 9hp. In this scenario, 1 extra melee power is better than 1 extra hp. This might not be the case when we're using an epic summoner or daria, but if you're using another summoner, then a different tank is probably going to be better anyway.

For the ability slowing (who is very bad for you in reverse speed by the way) he loose 1 speedpoint and one 1 lifepoint.

I used to think so too but then my level 5 clay golem + level 5 divine healer got smashed by the opponent's level 5 clay golem + level 6 givine healer. Why? Because I attacked first, so his golem was enraged when it attacked while mine wasn't. The irony. So I've come to conclusion it is better at level 6 specifically thanks to the clay golem card.