I am sure Hurricane 12 and others will weigh in.
I will comment on promotion rates - there is no way of knowing how that will go from year to year. It's a numbers problem: needs of the Marine Corps (including need for pilots in a given airframe), retention statistics for any given rank and year group (all those commissioned in a given fiscal year).
It has always been true that when phasing out and transitioning to a new airframe, some individuals will not get the opportunity to re-train for the new airframe. Their upward mobility will be impacted. We had a USNA sponsor daughter who was one of the last to fly Marine CH-46s. She ensured she was a top performer and laid her plans carefully to ensure she laterally transferred to another professional community where she was promotable. Fortunately for her, she was in a year group where she had flexibility. Some in more senior groups don't have as many options. This is where decisions made for the good of the service can derail the plans of individuals. In the Navy, P-3 to P-8 is currently having an impact, just as F-14 to F/A-18, diesel boat sub to all-nuke subs, and many other situations, have impacted careers over the years.
If you perform well as a pilot, meeting all professional qualifications, do your ground job well, maintain physical fitness standards, don't get into any misconduct situations, rank high amongst your peers, and serve in career-viable positions, you should be promoted. That is common to any service, any job. The first two promotions, to 1st lieutenant and captain, do not require a competitive promotion board, simply the CO's recommendation on your performance reports. The promotion to major, some 8-9 years from commissioning, is a statutory competitive board. The competition is serious by then. At every promotion board after that, as it is in all the services, the percentage of officers selected for promotion drops significantly. The services are only allowed to have X numbers of officers at any given pay grade, and thus set only Y targets for promotion numbers. Perfectly good officers with excellent records, at some point, will not get promoted, simply because of the competition. Theoretically, only truly outstanding officers with impeccable records AND with skill sets desired by their service, survive each successively more stringent round of promotions. The good news is, you will have amassed a professional resume that will equip you well for civilian employment, because everyone gets out at some point, even generals and admirals.