While it ultimaltey will make the ones with the higher attribute total better, the question also becomes: how often is or will this be a problem? And this is related to how long campaigns people run, how long characters survive; in most games I'd think that it doesn't matter much. A really long campaign, with a generous GM awarding XP liberally and often, yeah, it may become an issue.
But consider this: how many sessions do you play per month, over how many months are your campaigns usually last? How many XP is usually awarded? Total that up and then see how much or if it's a problem. If players know how many XP they will end up on in the end with - not something I tend to inform them of, but it is a nice thought experiment - they will design their characters in light of that. Let's say you intend to run a short campaign, of about 8 sessions, assuming 5 XP per session that is no more than 40 XP. 40 XP is 8 skill ranks, or a few skill ranks and some talents.
Now let's say you run on average a session every other week, holidays and all included, that's 26 sessions in a year - which to most will be a decent, perhaps even a good and long campaign. That's a total of 130 XP if you award them an average of 5 per session. Even my last long campaign, a year and a half and about 46 sessions (I believe), would result in about 230, perhaps a bit more if you are generous, let's say 250, that's averaging more than 5 XP per session. In this case you may, perhaps, be feeling it... but considering the number of skills and talents... and that the mortality rate of this game is pretty high... I'd not really worry.
The good thing about locking attributes is that not all characters get all 5s in the attributes, or at least very similar attribute lines. There are natural differences and variations in nature and innate ability.
"Life is like a sewer. What you get out of it, depends on what you put into it."
Make sure your brain is engaged before putting your mouth into gear.