I'm a Raichu user, and sorry, you're getting the priorities of a Raichu user all wrong. Raichu needs full Attack stat(s) and full speed.Raichu can never get higher than 229 for it's defense stat and 284 for it's special defense stat. Plus it's health can never go higher than 324. so lets say this Raichu was perfect IV for all stats giving it the max in health 230 AND it perfect EVed in HP giving it the 324HP (went up from 230) AND it was perfect EVed in Special Defense giving it the 284 stat. The last 1.5 point (6 points of EV) went to defense Oh Raichu also has a Gentle nature (Special Defense +, Defense -). And lets say it was using Choice Specs which now gives Raichu 324 Special Attack (since Raichu didn't train in special attack with EV training it would only get 185 as it's special attack stat at level 100, but since it has perfect IV's in all stats that gives a 31 point boost to this number giving it a final 216 special attack base stat. Choice specs only increases special attack by 50% of what the pokemon has. So do the math, 216/2+216=324. So stats would look like this
Spec. ATT: 436
Spec. DEF: 125
Spec. ATT: 324
Spec. DEF: 284
As you can see from the numbers Pikachu is faster then Raichu by 1 point!!!! And it would benifit Pikachu to use ONLY special attacks because they would far out weigh the damage it would do in comparassion to it's special attacks. Lets do some more math, the best possible situation here
Pikachu chooses to use Echoed Voice which IS a special attack. That is 436+100 in power! And since it is a neutral attack to electric type Raichu it's going to do 536-284=252 damage which leaves Raichu with 72HP if it did not crit. If the damage crit, then it's a 1 hit KO. Okay Now lets say Raichu survived and it wasn't a critical hit and Raichu used Hyper Beam 342+150 in power! and since it is also a neutral attack to electric Pikachu it's going to do 492-125=367 damage which will undoubtedly KO Pikachu with or without a critical hit, HOWEVER Hyper Beam has a 10% miss rate and if we factor into the equation the 35% increase in dodging skills if the Pokemon (any) are maxed out in Pokemon Aime (all hearts and notes and food) and in happiness we have Hyper Beam being very unlikely of hitting, besides looking into the coding of all the games Hyper Beam actually has a 75% change of hitting at base (don't believe me go tare the coding apart for yourself) Pikachu wins this battle more times than Raichu does.
This was just one scenario and even in this scenario Pikachu wins most of the time because BECAUSE Pokemon Aime maxed out for Pikachu increases the % chance of critical hits as well as a number of other things.
Over all statistically (not looking at stat values only) Pikachu WITH AND ONLY WITH Light Ball wins the majority of the time.