The "thumb notch" on the 98, while it may have served some purpose as a "thumb notch", was designed as a gas escape route by Mauser to allow gas to ecape the left raceway.
There is little doubt though, actions with out the notch are smoother in operation than those with it and are easy to work with as far as feeding is concerned.
The splitting of the left locking lug is something which I considered to be a bit of a flaw early in my career and was reason enough to look down a bit at the '98. Now that I've been gunsmithing for over 30 years, I've seen hundreds, if not thousands, of rifles built on Mauser actions and have come to realize this is not an issue. The slot, coupled with the very well designed bolt stop/ejector provides positive ejection to the side while having little effect on the strength of the action.
I am also a fan of the Ruger action (not a fan of their stupid trigger design mind you) but, if one wants a classic 50's styled sporter, he wants to use a Mauser. Regards, Bill.