The effective counter against mashers is to bait and punish their mashed reversals with your best combo.
Grabs will beat pokes if they startup before the startup of the poke and reach the poke’s hurt box. Grabs have a startup of 3 frames, so as long as you don’t leave a gap in your block string that is 3 frames or larger, than your opponent wouldn’t be able to mash throw and would eat a counterhit instead, AKA a frame trap.
Turtling is a viable strategy that works well only if the player has a good knowledge of the timing and range of their pokes, anti-airs, and projectiles to not just keep the other character out but to also hold their own ground as to not walk themself into the corner.
There’s a 3 frame window to tech grabs, and command throws have a ton of whiff recovery making them easy to bait and punish with neutral jumps and back dashes.
But really, the best thing for any new player to do once they have a good grasp on how to play fighting games is to stop playing against random mindless players in ranked altogether. Find decent players that are looking to get better in the online matchmaking subforums and add them to your friend’s list, or better yet find a local offline scene in your area.
There’s not much else you can do when most new players in the SF4 generation learn how to mash reversals and crouch tech before they learn how to properly block, developing bad habits thanks to the lenient inputs, lenient input windows, low block stun on normals, and mediocre netcode with the US’s mediocre internet infrastructure.