Um, mobilizing more people just means a lot more bodies get stacked.
The mismatch between Chinese irregulars and foreign troops with machine guns and HE artillery meant the Boxers only hope was the modern troops would get so sick of slaughtering unarmed fanatics they'd quit, or inconveniently run out of ammo and be overrun as Chinese Gordon was in the Sudan.
Unfortunately, the various foreign troops were mostly in coastal enclaves with good LOS, so unless the Boxers could sucker the foreign troops to go inland, they were screwed. Direct assault would just be a Grand Guignol slaughter.
In the short run, you could get a national movement that could try like hell to expel the foreigners. They'd succeed temprorarily, then the political bloodbath enusues as factionalism rears its ugly head and the economy spirals into the abyss.
Think purges and Year Zero nuttiness of Pol Pot's regime across China.
Refugee crises, famines, looting, banditry, plauges, disease, and suffering.
IOTL the foreign nations had severe problems getting all eleven foreign legations to coordinate strategy, tactics, logistics, and so forth.
The more modern Chinese forces stayed out of it b/c they realized it was suicide AND local commanders wanted to be around to pick up the pieces.
Unfortunately, they became the warlords that plagued China throughout the Republic of China's mainland existence.
The trouble that faced China from 1860-1945 is that there was no good answer.
The Qing were corrupt, behind the times, and didn't take the foreign threats seriously enough.
Also, the whole idea of the Middle Kingdom begging for help turned them off, so there was no foreign power that could or would stand with them.
The ROC founded by Sun-Yat-Sen said the right things and largely meant them, but the military strongmen supposed to enforce order decided they were supposed to run it themselves to disastrous results with Yuan Shikai and Chiang Kai Shek.
Even Mao's group was disastrous what with the Great Leap Backward famines, Cultural Revolution chaos, etc.
So much sad and unnecessary suffering for the Chinese people it beggars description.