Give the paladin the ability to heal himself with holy light

No, not a monster, but just a little stronger because now the AM+MK+PALA stratum is inferior in strength to the dk+lich+vampire stratum. This will largely equalize their strength, as it should be.

Making pala’s holy light usable on himself will just make standard hu hero choice am-mk-pala just overpowered.

No. The stratum Pala+Mk+archmage or pala+archmage+MK will be added. This is an increase in the variety of strats and an increase in the variety of strategies in the game.

At the same time, Palladin will not become a monster because his ultimate is countered by DK’s ultimate. When they both begin to reach level 6, the outcome of the battle in some cases will depend on who is the first to resurrect the dead on the battlefield. But a palladin can only resurrect his own, and DK can also resurrect strangers, and this will prevent the palladin from resurrecting his own.

If u want him as first hero - u need to suggest rework, not straight buff to his main ability what already used by him in support role.

What kind of “skill rework” are you proposing?
The palladin’s main problem, why he cannot be chosen as the first hero, is that he is a melee warrior who quickly loses health, and he does not have the ability to quickly heal himself. If the inability to heal oneself is his main drawback, then that is what needs to be corrected.
How do you propose to “rework” his skill so that it closes his main drawback of the inability to heal himself, which leads to the inability to choose him as the first hero?

Just tel me HOW win human with am aura, mk’s hammer plus 3rd pala with divine shield + holy light what he can use on himself plus few mana pots? This is sound super overpowered.

Easily. It is enough to simply prevent him from raising his heroes to such a high level, by imposing, for example, building up towers, or pushing an all-in push on T-2. The third level palladin always appears when approximately 70-80% of the game time has passed.
And even if he appears, this does not negate the fact that his ability to heal himself and his units is destroyed by burning the mana of the demon hunter, blood mage, and spell breaker.

In addition, the economy of the human race is always the most vulnerable to destruction because people cannot protect their workers from physical and magical damage.
Even if the heroes of people become stronger, this does not change the fact that the economy will remain just as vulnerable, and it will be just as easily destroyed by a combination of DK+lich, seer+tauren, or solo Varden heroes.

I see pala as first pick with changes like aura with 1 armor per rank but + 0.5 hp regen per rank

I already suggested this in my topic about changing the paladin

If this is not suitable, then instead of protection from magic, you can add to the aura a bonus to the health regeneration rate like the aura of a death knight, but less than that of a death knight. This, to some extent, will be a counter-measure against the disease of the undead, and human priests will not have to spend mana on treating their allies infected with the disease when mana is low.