Sorry, I've no idea what point you are trying to make.
The example you gave above is bizarre - a taxpayer earning €10k doesn't pay the same amount of tax as a taxpayer earning €50k.
Oh dear, you do realise that it was an example to illustrate the point. But just in case you cant figure that much out, lets apply real stats.
Two workers, one on €30,000 and one on €20,000. Both pay 20% on their incomes (€6,000+€4,000 - €10,000 in total). The higher earner (representating the top 50% of income earners) pays 60% of the tax take contributed between them. The lower earner contributes 40%.
Apply a personal tax credit of say, €2,000. Now the total tax take is reduced to €6,000 (€4,000+€2,000). But the % contributions have increased for the higher earner to 66% and reduced for the lower earner from 40% to 33%.
Add a third earner on €40,000, paying 40% on the €10,000 above €30,000.
Initially his total tax contribution is €10,000 ( €30,000@20% - €6,000 and €10,000@40% - €4,000.
This brings total tax take to €10,000+€6,000+€4,000= €20,000.
Now the top earner (representing the top 33%) contributes 50% of the total tax while the other 66% of earners contribute 50% also.
Throw in the personal tax credits of €2,000 each then the total tax take is reduced to €8,000+€4,000+€2,000 = €14,000. Of which the top 33% of earners now contribute 57% of the tax whilst the other 66% only contribute 43% between them.
Add a fourth worker on €50,000 and the process continues to diminish the % contribution of lower earners while increasing the % contribution of higher earners giving the impression that low paid workers dont pay their fair share.
The fact is, even if you earn €150,000, your tax contribution to public finances on your first €20,000 of that income is the same as someone who only earns €20,000 in total.
The rest of your tax contribution on the remaining €130,000 is not comparable with someone on €20,000 as they dont have that income to be taxed in the first instance.
And what is being proposed is a transfer of some of the tax liability of €130,000 to the earners on €20,000.