Both movies take place after the TV series featuring an OP character and the cast dealing with another threat of the day. What both have in common as well is the potential production of the next season while the light novel is ongoing. The only difference is that SAO movie is for both anime and ln fans whereas IAMGHS movie is meant to be for ln fans but accidentally anime fans.
The battle system in Ordinal Scale kinda reminds me of P3 Movies, where they fight the "monsters" in a specified time. The main characters also have to deal with similar problems, such as "bond" and "memories". You willl find more similarities in them if you watch P3 Movies till the last part.