There was always a limit to the blocked numbers. In previous iOS version, you were stilled allowed to add a number to the block list, but it did not actually work to block that contact when over the limit. That was confirmed by many in the posts you can find here on this Support Site. That bug was fixed, and now you see the limit message when attempting to block a number over the limit. What you need to do is get your blocked contacts to under 3,000.
Users likely did not even know that their blocked numbers beyond the limit were not working because spammers rarely would ever use the same contact again and the numbers provided are just "spoofed" where you would not even have a call from that number. That was also the case for you.
If you are using call blocking because you think that is used for spam control, it is not for the exact reason described. For Spam control, you should be using Call Screening and I would suggest the Ask Reason for Call option. That way spammers are not going to provide their name or reason for the call so your phone will not ring and legitimate calls from those not in your contacts will still come through as they would have no problem giving their name and reason for the call.
The only time where Call Blocking is effective is when blocking contacts from friends, family, or other legitimate numbers, and in that case it is not likely you would ever have over 3,000 of them.
You can certainly change to any other platform you wish and no one here would care what you do. But, if the fix in call blocking is the reason, then you did not understand that it was not working like you thought it was before and should probably base your decision to change platforms on something else entirely.
User level: Level 1 (4 points)
