"I think they happen way too early
"
I totally agree with you Rosbjerg !
Historically Polybian reform came around 230-220 BC just before the second punic war. So in game this means the triggering may reasonably come between turn 192 and 232 !(remember DEI great campaign begins in 278 BC and it is 4 turns a year)
Marian reform came around 100 BC. So when playing historically that means waiting about turn 712 to make it triggering....
Shall I talk about the Imperial reform or is it enough for you meerkatology ?
WTF are you talking about when you said that roman reforms come too late ?
At H/H level or even harder with your armies based on camillian reform (the basic one) you can keep back all the barbarian and greek factions during nearly half a century !
And with units based on polybian reform you can nearly challenge and dominate all type of ennemies during more than a century !
Maybe the issue is not so much about the way DEI triggers reform but as it is the way you're playing it ! Is it ?