Changed companies under AC21 after 180 days of I-485 pending. Previous company did EB2 to EB3 downgrade (new filing, not amendment) so have both approved EB2 I-140 and EB3 I-140.
Now that EB2 dates are moving faster, new company immigration lawyer is saying that I need to refile EB2 I-140 from scratch with new company including prevailing wage determination, PERM, and I-140. Only when EB2 I-140 is approved with new company, can I leverage EB2 final action dates. Stuck in this situation on whether to wait in EB3 (dates not moving), file a new EB2 with new company (can take 1.5 years plus), or go back to previous company which has EB2 I-140 approved already.
So you dont trust your immigration lawyer? 
PERM and I-140 are employer specific. PERM job sponsoring employer need to establish the basis and qualifications of the beneficiary for the PERM job and so I think your lawyer is correct that your current employer may not be able to establish the basis of EB2 job unless they file your PERM even though they can take over your GC process by filing I-485J which only establishes the basis of the already filed I-485 in the specific EB category.
You might want to consider going back to your EB2 sponsoring employer to be able to interfile EB2. Actually it is better to file a new EB2 I-485 after going back to your EB2 employer as interfile process do not always work 100% of time and is discretionary. Also interfile process is not really documented in the UCSIC policy documents as far as I know, so no specific guidelines for the processing officers.