Mysql – Is it a good practice to use index hints in production code

I would also test this rewriting (aasuming that sID is the primary key of docSVsys):

SELECT COUNT(*)              
FROM [docSVsys] AS d
WHERE EXISTS
      ( SELECT * 
        FROM [docSVtext] AS sv
        WHERE sv.[sID] = d.[sID] 
          AND sv.[value] = 'doug'
      )
   OR EXISTS
      ( SELECT * 
        FROM [docMVtext] AS mv
        WHERE mv.[sID] = d.[sID] 
          AND mv.[value] = 'doug'
      ) ;

There are many many many more factors at play.

• isolation level. locking behavior differs wildly between isolation levels. Some don't lock at all (read uncommitted, snapshot, rcsi). The default read committed transiently locks rows it reads as long as is necessary. Repeatable read and Serializable hold on to locks and end up locking everything, and many developers deploy serializable without ever realizing they do so.
• scan purpose. Scans for read are compatible with each other so they don't block, no matter what they lock. If you have scans blocking other scans they must be scans for update, which are incompatible with each other. Again, snapshot isolation level (including rcsi) do not block even when doing a scan for update.
• lock granularity, based on cardinality estimates. Scans may choose row, page or rowset level granularity. A table scan will likely choose page locks.
• index page locks/row locks configuration, which you so inadvertently changed. You should revert the change, since is not based on any measurement and root cause analysis. Guts feeling has no role in investigation.
• lock escalation
• row stability requirements when off-row LOB data is present
• other

I suggets you follow the procedure described in Capturing wait stats for a single operation to capture the wait stats of the scans you observed as blocking. Se if indeed they block on locks held by the table scan operation. IF the scenario is truly as you described (read scan vs. other read operations) then there is no reason for blocking so something else will be at play. You can also give sp_whoisactive a shot.