Not exactly true, you could easily create config like:
Advanced Routing Failover without Scripting
which relies on known gateways, but you can update those from DHCP client’s lease script (the example is in fact more complicated than necessary, it’s possible to use much simpler variant).
What I don’t like about linked config is that it usually relies on random third-party addresses like Google’s public DNS servers, so it’s kind of abuse. It would be also loads of fun, if they one day decided to block ping. 
From this point, using MikroTik’s internet detection is cleaner solution, as it’s made for this. But it would be even better, if they added an event which would fire when something changes, same way as lease script does.