What your lawyer might be saying it might be true, that there were lot of EB2 filing in june- july period, but that shouldn't really hamper any of EB2 movement.
Say, if most of the june- july filers were first time filers, their PD's will be that of 2006-2007, because Eb2 was current till 2004-2005. Now, if it was filers from pre 2005, it would mostly be BEC filers. Now with BEC filers, most of them were EB3, because earlier before the retrogession started, being EB2 or EB3 was very much the same, it really didn't make much of a difference.
Among the BEC filers there will be very few who would be refiling as EB2, for that either they had to withdraw their case from BEC and refile as EB2 under perm, and if the application would be accepted, then they could retain their earlier priority date, and for the case to be reviewed and approved it used to take over a year atleast. So, I doubt if there were too many of such cases. Then there was another method, i.e to get I-140 approved and use the PD portability law. For that to happen, after I-140 is approved, one has to file and start a complete new case all over again. I-140 itself used to take good time to get approved, and the whole process is quite complicated, its easier to wait for Priority dates to move than go for it, there wouldn't be many employers willing to go through such procedures and refiling for the same candidate. And then there were some BEC ppl whose came out early from BEC Q, when they filed for I-140, most of them must have mentioned AOS rather than CP, with bulletin Priority dates sliding to and fro, most of them didn't want their file sitting in consulate for yrs, most of them wanted to avail EAD option.
So most of the EB2 filers in June july are from the current crop of recent filers, so that shouldn't really effect the PD date movement, in next few yrs this massive EB2 filing will have its effect, not now.