I explained elsewhere:
Caster level is very important, and so is gaining access to higher level spells. A level 10 sorcerer has access to level 5 spells, while a 5 Sorc/5 Wiz casts at level 5 and only has access to level 3 spells.
If we're talking about 5th edition then that's not true at all. PHB Multiclass Spellcaster page 164-165. So you are incorrect.
Plus in 5th edition if you are multiclassing it's better to do it as 2 or 3 level dips of your non-main class. A 5 wizard/5 sorc is just a waste of level resources. The same would be true of two spell caster classes even if they synergized their spell casting stat.
Also, Wizards are INT-based while Sorcerers are CHA-based.
Which is only possibly important, not necessarily important. It really depends on what spells you choose. A paladin can afford to have low cha since most of a paladin's spells do not check the paladin's cha mod. Furthermore since the primary stat generation method in 5e is rolling for stats. It's completely possible to have both cha and int as high stats.
There are much, much better ways to improve the sorcerer's small spell list without wasting 2 levels on wiz.
Like I said it'd be better to run sorc 2 and wizard X rather than the other way around.