[...]
The thing about the expertise skills now is that you don't need to develop them forever. For example, +50 in Footwork is generally going to be plenty. +75 in Multiple Attacks gets you that second attack.
And having +100 AND an additional +50 in OB gets you a third.
So, yes, the pure fighter is going to be a better fighter, but that's not a valid comparison because the pure fighter doesn't have the magic. [...]
But what you said about fighter skills applies to Magic just as much: Having the tiniest amount of healing magic will go a long way for the pure Fighter, and of course he will have all kinds of magical artifacts that amount to the same thing as knowing magic intrinsically.
You should be comparing the fighter/healer to a corresponding semi profession; a semi is also going to have a very limited set of expertise skills, and I think the fighter/healer is surpassing that. The fighter/healer is also surpassing them significantly in number of spell lists. Extreme specialization will always pay off, it's the semis that are rendered irrelevant and inferior by changing professions.
Except the, say, "Combat Medic" class I just made up as a semi between a Fighter and a Healer can do BOTH magic and combat skills improvement EVERY level, instead of switching professions every other level. Depending on the type of campaign, it may take a lot of actual play time between levels, which means the profession switcher will have to a be a lot more patient AND will be especially at a disadvantage when it comes to Open lists of their realm or realms.
A Combat Medic at level 20 will know a few Open lists and his Base lists (which may be a bit smaller in scope than actual Healer lists, but still more powerful at level 20 than Healer lists at level 10) up to level 40 (though overcasting at -400 isnÄ't something I'd recommend, there are all kinds of circumstanes where that knowledge can be helpful). The profession switcher will only be able to get to level 20 at max, and if he wants to use his DP efficiently, he will only know them to level 10.
Seriously, guys. Try. It. Out.