This is the last thing you should be focusing on in CC
What the heck is the difference to you anyway?
Are you really that anxious to make people spend gems on revive?
Do you think that virtually 100% of the time they're attacking you because they WANT to attack you rather than because they HAVE to?
Do you really think your proposal would do anything to make any significant percentage of them stop?
This seems a weird and not at all useful combination of silly and petty.
By the way, I leave no heroes on my base when it's not GW day. Get a nice 100% almost without exception. Better than a bunch of 25 and 15%'s that do absolutely nothing for me and leave me with fewer resources in the long run, to boot.
The difference between having spells and not having them is time. Not everyone has all day to go raiding. Spells speed things up because you have to worry about losing a hero less. If you don't believe in spells, by all means, don't use them!
Another note is that no matter how experienced you are or how strong your heroes are, you will eventually lose one either by chance or a lapse in concentration. You don't want to have to spend 10 gems or wait 8+ minutes for that hero to revive, do you? Spells are much safer. Many experienced people use them just to make the odds of losing a hero even lower.
It's to balance the advantage defenders have maybe? Not to mention not everyone has all heroes and they have to raid too you know? Even if they were unlucky and have decent but not the best heroes? Because how is it "cheating" using magic when the advantage you get is a 50% buff to your heroes? How would it be fair if they had to go up with their 6 heroes VS your 6 but yours basically function as 9? -_- a bit weird if you ask me. I pretty much always raid to full and people can go ahead and raid me. They need it for quest boards too. Or would you rather be stuck with 100-200K raids when you need to do 3m+ for the gems or need to do 1M+ for a quest. Heck getting 3-4 3 star raids would be a nightmare as you would have to actively hunt for much weaker players only. And with them constantly in shields I can assure you it would be much harder to find a raidable base.
So no. Silly idea. Not everyone has Anubis, not everyone has Mino. This game needs to be playable by all. Not just you